Translucent substrate, process for producing the same, organic led element and process for producing the same

ABSTRACT

The present invention provides an organic LED element in which the extraction efficiency is improved up to 80% of emitted light. Further, the invention relates to an electrode-attached translucent substrate having a translucent substrate, a scattering layer formed over the glass substrate and containing a base material having a first refractive index for at least one wavelength of wavelengths of emitted light of an organic LED element and a plurality of scattering materials positioned in the base material and having a second refractive index different from that of the base material, and a translucent electrode formed over the scattering layer and having a third refractive index equal to or lower than the first refractive index, in which distribution of the scattering materials in the scattering layer decreases from the inside of the scattering layer toward the translucent electrode.

TECHNICAL FIELD

The present invention relates to a translucent substrate, a process forproducing the same, an organic LED element and a process for producingthe same, and particularly relates to a light-extraction structure of anorganic LED (organic light emitting diode) or the like.

BACKGROUND ART

An organic LED element is one in which an organic layer is put betweenelectrodes, and a voltage is applied between the electrodes to injectholes and electrons, which are allowed to be recombined in the organiclayer, thereby extracting light that a light-emitting molecule emits inthe course of transition from an excited state to a ground state, andhas been used for display, backlight and lighting applications.

The refractive index of the organic layer is from about 1.8 to about 2.1at 430 nm. On the other hand, the refractive index, for example, at thetime when ITO (indium tin oxide) is used as a translucent electrodelayer is generally from about 1.9 to about 2.1, although it variesdepending on the ITO film-forming conditions or composition (Sn—Inratio). Like this, the organic layer and the translucent electrode layerare close to each other in refractive index, so that emitted lightreaches an interface between the translucent electrode layer and atranslucent substrate without totally reflecting between the organiclayer and the translucent electrode layer. A glass or resin substrate isusually used as the translucent substrate, and the refractive indexthereof is from about 1.5 to about 1.6, which is lower in the refractiveindex than the organic layer or the translucent electrode layer.Considering Snell's law, light which tries to enter the glass substrateat a shallow angle is reflected by total reflection in an organic layerdirection, and reflected again at a reflective electrode to reach theinterface of the glass substrate again. At this time, the incident angleto the glass substrate does not vary, so that reflection is repeated inthe organic layer and the translucent electrode layer to fail to extractthe light from the glass substrate to the outside. According to anapproximate estimate, it is known that about 60% of the emitted lightcan not be extracted by this mode (organic layer-translucent electrodelayer propagation mode). The same also occurs at an interface betweenthe substrate and the air, whereby about 20% of the emitted lightpropagates in the glass and fails to be extracted (substrate propagationmode). Accordingly, the amount of the light which can be extracted tothe outside of the organic LED element is less than 20% of the emittedlight in the present circumstances.

Patent document 1 proposes a structure in which a light scattering layeras a translucent material layer is provided on one surface of asubstrate (paragraphs 0039 to 0040). This proposes a structure in whichglass particles are firmly fixed to the surface of the substrate with anacrylic adhesive to perform an aggregation arrangement on the surface ofthe substrate, thereby providing a light scattering portion between thesubstrate and an organic EL element.

Further, intending to improve extraction efficiency, patent document 2discloses “an organic EL element comprising a translucent substratehaving provided thereon a scattering layer comprising an additionallayer composed of a transparent material in which SiO₂ particles, resinparticles, a metal powder or metal oxide particles are dispersed, by aresin-based adhesive, spraying, vapor deposition, sputtering, dipping,spin coating or the like” (paragraph 0057).

Patent document 3 discloses a light-emitting device in which a diffusinglayer obtained by dispersing at least two kinds of fine particles onedigit or more different in average particle size in a resin is providedadjacent to a translucent electrode, thereby efficiently extractingwave-guided light.

Further, patent document 4 proposes a technique of preventing totalreflection in the inside of a display formed by using a light-emittingdevice, thereby intending to increase luminance. In patent document 4,it is described that “a high diffusion material may be coated on a layerof a light-emitting device such as a substrate, a transparent electrode,an optical film or another component (patent document 4, paragraph0027), Furthermore, it is described that “for example, particles may bearranged in glass frit, suitably coated, flattened and fired to form aglass substrate or a layer on a glass substrate, which acts as a highdiffusion TIR frustrator” (patent document 4, paragraph 0027).

Moreover, also in patent document 5, paragraph 0026, there aredescriptions similar to those of patent document 4.

Patent Document 1 Japanese Patent No. 2931211

Patent Document 2 JP-A-2005-63704

Patent Document 3 JP-A-2005-190931

Patent Document 4 JP-T-2004-513483

Patent Document 5 JP-T-2004-513484

DISCLOSURE OF THE INVENTION Problems That the Invention is to Solve

However, in patent document 1, paraffin or the like is fixed as thetranslucent material layer onto the substrate with the resin binder(paragraph 0040). Namely, the light scattering portion of patentdocument 1 is the resin, and liable to absorb water. Accordingly, theorganic EL device of patent document 1 has a problem that it can notwithstand use for a long period of time.

Further, patent document 2 discloses that the refractive index of thetranslucent substrate is brought near that of the scattering layer.However, it makes no mention of the relationship between the refractiveindex of the scattering layer and that of a translucent electrode layerat all. Further, patent document 2 discloses that a surface of thescattering layer may be uneven, in a text of the specification.

Further, patent documents 3 and 4 suggest use of the glass layer whichis decreased in high-temperature degradation and stable, but makes nomention of unevenness of a surface of the scattering layer at all.

When the surface is uneven herein, the unevenness tends to be formed ona surface of a first electrode formed on this upper layer. When a layerhaving a light emitting function or the like is formed on this upperlayer by a vapor deposition method or the like, coatability of theorganic layer to the unevenness deteriorates, resulting in theoccurrence of variation in thickness of the organic layer. Further, as aresult, variation occurs in interelectrode distance between theabove-mentioned first electrode and a surface of a second electrodeformed on the organic layer. As a result, it has been known that in aregion small in interelectrode distance, a large current locally flowsthrough the organic layer to cause an interelectrode short circuit,leading to non-lighting. Furthermore, when a display device constitutedby fine pixels such as a high-resolution display is formed, it isnecessary to form a fine pixel pattern. There has been a problem thatnot only the unevenness of the surface contributes to the occurrence ofvariation in position of pixels and size, but also an organic element isshort-circuited by this unevenness.

As described above, none of the above-mentioned patent documents 1 to 5has made mention of the flatness (arithmetic average roughness) of thesurface of the scattering layer. Further, none of the patent documentshas shown an example of preparing the scattering layer by glass.

Further, the organic EL element is formed by laminating thin films, sothat angular dependency of color is high due to interference, which hasalso posed a problem that color is not exactly reproduced according to aseeing direction.

Also from such a viewpoint, demand for a translucent substrate having ascattering layer which is thin, high in flatness and further high inrefractive index increases.

An object of the invention is to improve light-extraction efficiency.

Further, in an embodiment of the invention, it is an object to provide atranslucent substrate having a scattering layer excellent in scatteringcharacteristics and having a desired refractive index, while keepingsurface smoothness.

Furthermore, in another embodiment of the invention, it is an object toimprove light-extraction efficiency to provide a high-efficient,long-life organic LED element.

In addition, in still another embodiment of the invention, it is anobject to provide an organic LED element which can inhibit angulardependency of color.

Further, in another embodiment of the invention, when a reflectiveelectrode is used as an electrode facing to a translucent electrodeformed on a translucent substrate, it is an object to provide thetranslucent substrate and an organic EL element in which the appearanceis not spoiled by the occurrence of reflection due to the reflectiveelectrode at the time of non-light emission.

Means for Solving the Problems

Accordingly, the electrode-attached translucent substrate of theinvention comprises a translucent glass substrate, a scattering layerformed on the above-mentioned glass substrate and comprising a glasswhich contains a base material having a first refractive index for atleast one wavelength of light to be transmitted and a plurality ofscattering materials dispersed in the above-mentioned base material andhaving a second refractive index different from that of theabove-mentioned base material, and a translucent electrode formed on theabove-mentioned scattering layer and having a third refractive indexequal to or lower than the above-mentioned first refractive index,wherein distribution of the above-mentioned scattering materials in theabove-mentioned scattering layer decreases from the inside of theabove-mentioned scattering layer toward the above-mentioned translucentelectrode.

Further, in the invention, in the above-mentioned translucent substrate,a surface of the above-mentioned scattering layer forms wavinessconstituting a curved surface.

Furthermore, in the invention, in the above-mentioned translucentsubstrate, the scattering layer includes one in which the ratio Ra/Rλaof the waviness roughness Ra of the surface of the above-mentionedscattering layer to the wavelength Rλa of the waviness of the surface isfrom 1.0×1.0⁻³ to 3.0×10⁻².

In addition, an organic LED element of the invention uses theabove-mentioned translucent substrate and comprises a layer having alight-emitting function formed on the above-mentioned translucentelectrode as a first electrode and a second electrode formed on theabove-mentioned layer having a light-emitting function.

Further, a process for producing a translucent substrate of theinvention comprises the steps of preparing a translucent glasssubstrate, forming on the above-mentioned glass substrate a scatteringlayer comprising a base material having a first refractive index and aplurality of scattering materials dispersed in the above-mentioned basematerial and having a second refractive index different from that of theabove-mentioned base material, and forming on the above-mentionedscattering layer a translucent electrode having a third refractive indexequal to or lower than the above-mentioned first refractive index,wherein the above-mentioned scattering layer forming step includes thesteps of applying a coating material containing a glass powder onto theabove-mentioned glass substrate and firing the above-mentioned appliedglass powder, and the intralayer distribution of the scatteringmaterials in the scattering layer decreases from the inside of theabove-mentioned scattering layer toward the outermost surface thereof.

The above-mentioned firing step includes herein the step of firing theglass powder at a temperature which is 60 to 100° C. higher than theglass transition temperature of the above-mentioned applied glassmaterial.

The electrode-attached translucent substrate (laminate for an organicLED element) of the invention comprises a translucent substrate, ascattering layer formed on the translucent substrate and comprising abase material having a first refractive index for at least onewavelength of wavelengths of emitted light of the organic LED elementand a plurality of scattering materials positioned in the inside of thebase material and having a second refractive index different from thatof the base material, and a translucent electrode formed on thescattering layer and having a third refractive index equal to or lowerthan the first refractive index.

The organic LED element of the invention comprises a translucentsubstrate, a scattering layer formed on the translucent substrate andcomprising a base material having a first refractive index for at leastone wavelength of wavelengths of emitted light of the organic LEDelement and a plurality of scattering materials positioned in the insideof the base material and having a second refractive index different fromthat of the base material, a translucent electrode formed on thescattering layer and having a third refractive index equal to or lowerthan the first refractive index, an organic layer formed on thetranslucent electrode and a reflective electrode formed on the organiclayer.

The waviness roughness Ra and the average wavelength Rλa as used hereinmean values calculated based on JIS B0601 (2001) (the translatedstandard of ISO 97), taking the short wavelength cutoff value as 25.0 μmand the long wavelength cutoff value as 2.5 mm.

Further, the surface roughness Ra means the microscopically observedsurface roughness and a value calculated in accordance with JIS B0601(1994), taking the long wavelength cutoff value as 10 μm.

ADVANTAGES OF THE INVENTION

According to the invention, the light-extraction efficiency can beimproved, and it becomes possible to provide a translucent substratewhich can provide an optical device having high extraction efficiency.

Further, scatterability can be increased, so that the angular dependencyof color can be decreased.

Furthermore, a scattering layer is constituted by glass, thereby beingable to realize stability and high strength, which makes it possible toprovide a translucent substrate excellent in scatterability withoutincreasing the thickness compared to an original translucent substratemade of glass.

According to the invention, an organic LED element can be provided inwhich the extraction efficiency is improved up to 80% of the emittedlight.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing structures of a translucentsubstrate and an organic LED element of embodiment 1 of the invention.

FIG. 2 is a schematic view showing a state of glass particlesconstituting a scattering layer of the translucent substrate ofembodiment 1 of the invention, at the time of coating.

FIG. 3 is a schematic view showing a state of the glass particlesconstituting the scattering layer of the translucent substrate ofembodiment 1 of the invention, at the time of firing.

FIG. 4 is a schematic view showing a state of a scattering layer attimes when fired at a temperature lower than the softening point of theglass as a comparative example of the invention.

FIG. 5 is a schematic view showing a state of the scattering layer (whenfired at a temperature sufficiently higher than the softening point ofthe glass) of embodiment 1 of the invention.

FIG. 6 is a schematic view showing a state of a waviness of a surface ofthe scattering layer of embodiment 1 of the invention.

FIG. 7 is a schematic view showing a state of a microscopic concaveportion of the surface of the scattering layer.

FIG. 8 is a schematic view showing a state of a microscopic concaveportion of the surface of the scattering layer.

FIG. 9 is a schematic view showing a state of the surface of thescattering layer of embodiment 1 of the invention.

FIG. 10 is a schematic view showing a state of a surface of a scatteringlayer of a comparative example (when the firing temperature is toohigh).

FIG. 11 is a graph showing the relationship between the light-extractionefficiency (%) and the content (vol %) of a scattering material.

FIG. 12 is a graph showing the relationship between the light-extractionefficiency (%) and the refractive index of a scattering material.

FIG. 13 is a graph showing the relationship between the light-extractionefficiency (%) and the content (vol %) of a scattering material.

FIG. 14 is a graph showing the relationship between the light-extractionefficiency (%) and the number (number/mm²) of scattering materials.

FIG. 15 is a graph showing the relationship between the light-extractionefficiency (%) and the transmittance (@1 mmt %) of a base material ofthe scattering layer.

FIG. 16 is a graph showing the relationship between the light-extractionefficiency (%) and the reflectivity (%) of a cathode.

FIG. 17 is a graph showing the relationship between the ratio of lightoutgoing to the scattering layer and the refractive index of the basematerial of the scattering layer.

FIG. 18 is a graph showing the relationship between the wavelength andthe refractive index of the base material of the scattering layer.

FIG. 19 show the results of a simulation of the relationship between thewavelength and the illuminance of a light receiving surface.

FIG. 20 is a flow chart showing a process for producing a substrate foran organic LED element of the invention.

FIG. 21 is a flow chart showing a process for producing an organic LEDelement of the invention.

FIG. 22 is a cross-sectional view schematically showing a constitutionof an organic EL display device.

FIG. 23 is a cross-sectional view showing other structures of a laminatefor an organic LED element and an organic LED element of the invention.

FIG. 24 shows the results of observation from the front under conditionsof sample 1 and sample 2.

FIG. 25 is a cross-sectional view taken along line A-A as seen from thedirection C in FIG. 26, showing a structure of an evaluation element.

FIG. 26 is a top view of the evaluation element seen from the directionB in FIG. 25.

FIG. 27 are graphs showing wavinesses of surfaces of scattering layers.FIG. 27(A) is a graph showing waviness of a surface of a scatteringlayer having a film thickness of 60 μm, and FIG. 27(B) is a graphshowing waviness of a surface of a scattering layer having a filmthickness of 60 μm obtained by polishing a scattering layer having afilm thickness of 120 μm.

FIG. 28 is a graph showing the results obtained by measuring a surfaceshape of a scattering layer with a surface roughness tester.

FIG. 29 are graphs showing the measurement results of local roughness ofsurfaces of scattering layers. FIG. 29(A) is a graph showing themeasurement results of a surface of a non-polished scattering layer, andFIG. 29(B) is a graph showing the measurement results of a surface of apolished scattering layer.

FIG. 30 is a block diagram showing the constitution of an evaluationsystem for evaluating light-emitting characteristics.

FIG. 31 is a block diagram showing measurement points.

FIG. 32 is a graph showing luminance distribution of a centrallight-emitting region 2210 and a peripheral light-emitting region 2220.

FIG. 33 is a graph showing the average front luminance of fivemeasurement points for each scattering layer changed in thickness.

FIG. 34 is a graph showing the luminance at the time when the five-pointaverage value is corrected by measuring the amount of light of aperipheral light-emitting region for each scattering layer changed inthickness.

FIG. 35 is a graph showing the ratio of the front luminance in a regionhaving no scattering layer and a region having a scattering layer ofeach evaluation element.

FIG. 36 is a graph showing the measurement results of fluorescencespectra of a region having a scattering layer and a region having noscattering layer.

FIG. 37 is a graph in which in the measurement results of thefluorescence spectrum of the region having a scattering layer, thespectrum of the region having no scattering layer, the intensity ofwhich is doubled, is overwritten on the spectrum of the region having ascattering layer.

FIG. 38 is a graph showing the measurement results of directionaldependency of light intensity.

FIG. 39 is a graph in which the data of FIG. 38 is normalized by frontlight intensity.

FIG. 40 is a graph showing pore diameter distribution.

FIG. 41 is a graph comparing the measurement results in the present caseto the relationship between the number of pores per 1 mm² and thelight-extraction efficiency at the time when the pore diameter is 2 μm.

FIG. 42 is a graph showing the refractive indexes of a glass for ascattering layer, an ITO film and an Alq₃ film used in an evaluationexperiment.

FIG. 43 is a graph showing the measurement results of the relationshipbetween the firing temperature and the surface roughness of a scatteringlayer of a translucent substrate in Example 2 of the invention.

FIG. 44 is a graph showing the measurement results of the relationshipbetween the firing temperature and the refractive index of a scatteringlayer of a translucent substrate in Example 2 of the invention.

FIG. 45 is a view showing a light-emitting state of an organic LEDelement formed by using the translucent substrate in Example 2 of theinvention.

FIG. 46 is a view showing a light-emitting state of an organic LEDelement formed by using a translucent substrate for comparison.

FIG. 47 is a graph showing the voltage-currant characteristic of theorganic LED elements formed by using the translucent subs-rates inExample 2 of the invention and for comparison.

FIG. 48 is a graph showing the current-luminance characteristic of theorganic LED elements formed by using the translucent substrates inExample 2 of the invention and for comparison.

FIG. 49 is a view showing a measurement device for measuring the angulardependency of light-emitting luminance and light-emitting color inExample 3 of the invention.

FIG. 50 is a graph showing spectral data of the angular dependency oflight-emitting luminance and light-emitting color of an organic LEDelement for comparison.

FIG. 51 is a graph showing spectral data of the angular dependency oflight-emitting luminance and light-emitting color of the organic LEDelement for comparison.

FIG. 52 is a graph showing spectral data of the angular dependency oflight-emitting luminance and light-emitting color of an organic LEDelement in Example 3 of the invention.

FIG. 53 is a graph showing spectral data of the angular dependency oflight-emitting luminance and light-emitting color of the organic LEDelement in Example 3 of the invention.

FIG. 54 is a graph showing the chromatic coordinates of the angulardependency of light-emitting luminance and light-emitting color of theorganic LED element in Example 3 of the invention.

FIG. 55 is a graph showing the relationship between the depth and thenumber of pores in a scattering layer of the organic LED element inExample 3 of the invention.

FIG. 56 is a view showing a method for measuring the transmittance of ascattering layer of Example 4 of the invention.

FIG. 57 is a graph showing the measurement results of the relationshipbetween the film thickness and the total light transmittance of thescattering layer of Example 4 of the invention.

FIG. 58 is a graph showing the relationship between the film thicknessand the haze value of the scattering layer of Example 4 of theinvention.

FIG. 59 is a graph showing the light-extraction efficiency ratio(light-extraction ratio) comparing the total light transmittance ofExample 4 of the invention to the case of having no scattering layer.

FIG. 60 is a graph showing the light-extraction efficiency ratio(light-extraction ratio) comparing the haze value of Example 4 of theinvention to the case of having no scattering layer.

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS

-   -   100 Electrode-Attached Translucent Substrate (Laminate for        Organic LED Element)    -   101 Glass Substrate    -   102 Scattering Layer    -   103 Translucent Electrode    -   104 Scattering Material    -   110 Organic Layer    -   120 Reflective Electrode

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1

The electrode-attached translucent substrate (laminate for an organicLED element) of embodiment 1 of the invention and the organic LEDelement being laminated for an organic LED element will be describedbelow with reference to the drawings. FIG. 1 is a cross-sectional viewshowing structures of the laminate for an organic LED element and theorganic LED element being laminated for an organic LED element.

The organic LED element of the invention comprises an electrode-attachedtranslucent substrate (laminate for an organic LED element) 100, anorganic layer 110 and a reflective electrode 120, as shown in FIG. 1.The electrode-attached translucent substrate comprises a substrate 101as a translucent glass substrate, a scattering layer 102 and atranslucent electrode 103.

The electrode-attached translucent substrate 100 used in the inventioncomprises the translucent glass substrate 101, the scattering layer 102including glass and formed on the above-mentioned glass substrate andthe translucent electrode 103. The above-mentioned scattering layercomprises a base material having a first refractive index at onewavelength of light to be transmitted and a plurality of scatteringmaterials 104 dispersed in the above-mentioned base material and havinga second refractive index different from that of the above-mentionedbase material, and the distribution of the above-mentioned scatteringmaterials in the above-mentioned scattering layer decreases from theinside of the above-mentioned scattering layer to the above-mentionedtranslucent electrode. This translucent electrode 103 has a thirdrefractive index equal to or lower than the above-mentioned firstrefractive index.

Further, the density ρ₁ of the scattering material at a half thickness(δ/2) of the above-mentioned scattering layer 102 including glass andthe density ρ₂ of the scattering material at a distance x (δ/2≦x≦δ) froma surface of the above-mentioned scattering layer on the side facing tothe above-mentioned translucent electrode (namely, a surface on thesubstrate side) satisfy ρ₁≧ρ₂.

Further, the density ρ₃ of the scattering material at a distance x(x≦0.2 μm) from the translucent electrode side surface of theabove-mentioned scattering layer including glass and the density ρ₄ ofthe above-mentioned scattering material at a distance x=2 μm satisfyρ₄>ρ₃. This is also clear from FIG. 55, although described later. FIG.55 shows the case where the firing temperature is 570° C. and 580° C.However, similar results could be obtained even when the firingtemperature was somewhat changed.

Furthermore, the density ρ₃ of the scattering material at a distance x(x≦0.2 μm) from the translucent electrode side surface of theabove-mentioned scattering layer including glass and the density ρ₅ ofthe above-mentioned scattering material at a distance x=5 μm satisfyρ₅>ρ₃. This is also clear from FIG. 55, although also described later.

According to this constitution, the probability that pores, precipitatedcrystals or the scattering material composed of a material different incomposition from the base material exists in a surface layer of thescattering layer as a glass layer and directly thereunder is lower thanin the inside of the scattering layer, so that a smooth surface can beobtained. For this reason, for example, in the case of forming anorganic EL element, a surface of the translucent substrate, namely asurface of the scattering layer, is smooth, so that a surface of thetranslucent electrode (first electrode) formed on this upper layer issmooth. Also in the case of forming a layer having a light-emittingfunction, or the like on this upper layer by a coating method or thelike, the layer having a light-emitting function can be uniformlyformed, and the interelectrode distance between the translucentelectrode and a surface of the reflective electrode (second electrode)formed on the layer having a light-emitting function also becomesuniform. As a result, it does not happen that a large current is locallyapplied to the layer having a light-emitting function, so that thelifetime can be prolonged. Further, when a display device constituted byfine pixels such as a high-resolution display is formed, it is necessaryto form a fine pixel pattern. There has been a problem that not only theunevenness of the surface contributes to the occurrence of variation inposition of pixels and size, but also an organic EL element isshort-circuited by this unevenness. However, the fine pattern can beformed with high accuracy.

Incidentally, although the scattering layer is directly formed on theglass substrate, it may be formed with the interposition of a barrierlayer, for example, such that a thin silica film is formed on the glasssubstrate by a sputtering method or the like, and then the scatteringlayer is formed thereon. However, an extremely stable and flat surfacecan be obtained by forming the scattering layer including glass with nointerposition of an adhesive or an organic layer. Moreover, it becomespossible to form a thermally stable and long-life optical device byconstituting it with only inorganic materials.

Characteristics of such a translucent substrate will be described indetail.

When a glass powder is fired, a schematic view of a state in which theglass powder is applied by a suitable method is shown in FIG. 2. A crosssection of an outermost portion of a glass layer as the scattering layerconstituting the translucent substrate of the invention is shown herein.This state can be obtained, for example, by dispersing glass particles Gin a solvent or a mixture of a resin and a solvent and applying theresulting dispersion to a desired thickness. For example, there are usedthe glass particle G having a size of about 0.1 to about 10 μm in termsof the maximum length. When the resin and the solvent are mixed, a resinmembrane in which the glass particles G are dispersed is heated todecompose the resin, thereby obtaining the state of FIG. 2. FIG. 2 isdrawn in a simplified manner, and there is a space between the glassparticles.

Supposing that the glass particle size of the glass particles G hasdistribution, it is conceivable that a structure in which a small glassparticle enters the space between the large glass particles G isobtained. When the temperature further rises, the glass particles startto be fused to one another at a temperature 10° C. to 20° C. higher thanthe softening temperature of the glass. A state at this time is shown inFIG. 3. When the glass particles are fused to one another, the spaceformed between the glass particles of FIG. 2 is deformed by softening ofthe glass to form a closed space in the glass. The glass particles arefused to one another, whereby outermost layers of the glass particlesform an outermost surface of the scattering layer 102 (glass layer). Onthe outermost surface 200, the space which does not form the closedspace is present as a depression.

When the temperature is further raised, softening and fluidity of theglass proceed, and the space in the inside of the glass forms aspherical pore. On the glass outermost surface 200, the depressioncaused by the space between the glass particles G is smoothed. Thisstate is shown in FIG. 4. Not only the pore due to the space between theglass particles G, but also pores are formed by generation of a gas atthe time when the glass is softened, in some cases. For example, when anorganic material is adhered to the surface of the glass layer, itdecomposes to generate CO₂, thereby forming pores in some cases.Further, such a thermally decomposable material may be introduced topositively generate pores. Such a state is usually obtained in thevicinity of the softening temperature. The viscosity of the glass is ashigh as 10^(7.6) poises at the softening temperature, so that the porescan not rise to the surface in the case where the size of the pores isseveral microns or less. Accordingly, it is possible to further smooththe surface while inhibiting the pores from rising to the surface byadjusting the material composition so as to generate small pores and byfurther raising the temperature or by prolonging the retention time.When cooled from the state in which the surface is smoothed in this way,the scattering glass layer is obtained in which the density of thescattering material is smaller in the inside of the glass layer than inthe surface thereof and which has a smooth surface.

Like this, it is possible to inhibit the generation of the pores anddepressions in the outermost surface of the glass layer while leavingthe pores in the glass layer by adjusting the material composition andfiring temperature for forming the glass layer. Namely, it becomespossible to provide the electrode-attached translucent substrateexcellent in scattering characteristics and high in surface smoothnessby adjusting the firing temperature profile and adjusting the firingtemperature so as to prevent the scattering material from rising and toleave the pores in the glass layer not to rise to the surface.

Further, at this time, the surface of the glass layer undulates in somecases depending on the treating temperature, the glass material for theglass layer, the size of the glass particles and the substrate material.A schematic view thereof is shown in FIG. 6. The waviness as used hereinhave a period of 10 μm or more. The size of the waviness is from about0.01 μm to about 5 μm in terms of the waviness roughness Ra. Even whensuch waviness is present, the microscopic smoothness, namely themicroscopic surface roughness Ra, is kept at 30 nm or less. When thetreating temperature is low, a microscopic concave portion of theoutermost surface is left in some cases. However, the shape of theconcave portion becomes gentle as shown in FIG. 8, not an overhung shapeas shown in FIG. 7. The overhung shape as used herein means that theangle θ between the surface of the scattering layer and a tangent linein the vicinity of an opening of the concave portion is an acute angleas shown in FIG. 7, and the term gentle means that θ in FIG. 8 is anobtuse angle or a right angle. When the shape is gentle as describedabove, it is said that the possibility that this concave portion causesan interelectrode short circuit of the organic EL element is low. Thefiring temperature is desirably about 40° C. to about 60° C. higher thanthe glass transition temperature. A too low temperature causesinsufficient sintering, resulting in failure to smooth the surface.Accordingly, the firing temperature is more desirably about 50° C. toabout 60° C. higher than the glass transition temperature.

Further, use of the easily crystallizable glass makes it possible toprecipitate crystals in the inside of the glass layer. At this time,when the crystals have a size of 0.1 μm or more, they act as a lightscattering material. A state at this time is shown in FIG. 9. A suitableselection of the firing temperature makes it possible to precipitate thecrystals in the inside of the glass layer while inhibiting theprecipitation of the crystals in the outermost surface of the glasslayer as described above. Specifically, it is desirable that thetemperature is about 60° C. to about 100° C. higher than the glasstransition temperature. On such an increase in temperature as this, theviscosity of the glass is high, and the pores do not rise to thesurface.

When the temperature is too high, the crystals also precipitate in theoutermost surface of the glass layer to lose smoothness of the outermostsurface. This is therefore unfavorable. A schematic view thereof isshown in FIG. 10. Accordingly, the firing temperature is more preferablyabout 60° C. to about 80° C. higher than the glass transitiontemperature, and most preferably about 60° C. to about 70° C. higherthan the glass transition temperature. Such a technique makes itpossible to allow the pores and the precipitated crystals to exist inthe glass layer as the scattering material and to inhibit the generationthereof in the glass outermost surface. The reason why these arepossible is that the glass is flattened for itself within the certaintemperature range, and that high viscosity at which the pores do notrise to the surface can be realized or the crystals can be precipitated.In the case of a resin, it is difficult to control the process at highviscosity as described above, and also the crystals can not beprecipitated.

As described above, the translucent substrate in which the density ofthe scattering material in the outermost surface of the above-mentionedscattering layer is lower than the density of the scattering material inthe inside of the above-mentioned scattering layer can be obtained byadjusting the material composition and the firing conditions.

Further, it becomes possible to obtain the translucent substrate havingsufficient scattering characteristics and a smooth surface by using atranslucent substrate in which there is present such δ that the densityρ₁ of the scattering material at a half thickness of the above-mentionedscattering layer including glass and the density ρ₂ of the scatteringmaterial at a distance x from a surface of the above-mentionedscattering layer on the side facing to the above-mentioned translucentelectrode (namely, a surface on the substrate side), which satisfiesδ/2≦x≦δ, satisfy ρ₁≧ρ₂.

Further, in the scattering layer, the surface forms wavinessconstituting a curved surface, thereby being able to inhibit theappearance from being spoiled by reflection, when the organic EL elementformed on the upper layer is a reflective electrode. When the reflectiveelectrode is used, it has been a problem that the appearance is spoiledby reflection due to the reflective electrode at the time of non-lightemission. However, according to the invention, the accuracy of a patternformed on the upper layer is not deteriorated, variation does not occurin interelectrode distance, and the contact area of the electrode andthe layer having a light-emitting function can be increased, by makingthe conditions suitable when the scattering layer is formed.Accordingly, the effective element area can be increased, thereby beingable to form the long-life, high-intensity organic EL element.

Furthermore, as shown in FIG. 6, the ratio Ra/Rλa of the wavinessroughness Ra of the surface of this scattering layer to the wavelengthRλa of the waviness of the surface is desirably from 1.0×10⁻⁶ to3.0×10⁻⁵.

In addition, the surface roughness Ra of the surface of theabove-mentioned scattering layer is desirably 30 nm or less. Moredesirably, the surface roughness of the above-mentioned scattering layeris 10 nm or less.

For example, when the organic EL element is formed on such a translucentsubstrate, for example, the translucent substrate is required to bethinly formed. It is at a surface roughness of 30 nm or less, desirably10 nm or less that this translucent electrode can be formed withoutbeing affected by a ground. When the surface roughness exceeds 30 nm,coatability of the organic layer formed thereon deteriorates in somecases, and a short circuit occurs between the translucent electrodeformed on the glass scattering layer and the other electrode in somecases. The interelectrode short circuit causes non-lighting of theelement, but it is possible to restore it by applying an overcurrent insome cases. In order to make the restoration possible, the roughness ofthe glass scattering layer is desirably 10 nm or less, and moredesirably 3 nm or less.

Incidentally, in a certain material system, it is known that a surfaceroughness of 10 nm or less can be obtained when the firing temperatureis adjusted to 570° C. or more (see Table 1). Although the optimumfiring conditions vary depending on the material system, the scatteringmaterial is inhibited from being present in the outermost surface bycontrolling the kind or size of scattering material, thereby being ableto obtain the scattering layer with an excellent surface smoothness.

Further, when the pores are present in the scattering layer, an increasein size of the pores increases buoyancy in a scattering layer formingprocess such as firing, resulting in an easy rising of the pores to thesurface. When the pores reach the outermost surface, there is thepossibility that they burst to significantly deteriorate the surfacesmoothness. Furthermore, the number of the scattering materialsrelatively decreases in that portion, so that scatterability decreasesonly in that portion. Coagulation of such large pores also results invisual observation as unevenness. Moreover, the ratio of the poreshaving a diameter of 5 μm or more is desirably 15 vol % or less, moredesirably 10 vol % or less, and still more preferably 7 vol % or less.In addition, even when the scattering material is other than the pores,the number of the scattering materials relatively decreases in thatportion, so that scatterability decreases only in that portion.Accordingly, the ratio of the scattering material having a maximumlength of 5 μm or more is desirably 15 vol % or less, more desirably 10vol % or less, and still more desirably 7 vol % or less.

Still further, when the reflective electrode is used, there has been aproblem that the appearance is spoiled by the occurrence of reflectiondue to the reflective electrode at the time of non-light emission.However, when the scattering layer is formed, the conditions areoptimized, thereby being able to form waviness shape on the surface ofthe scattering layer. The waviness of the surface of the scatteringlayer was measured. SURFCOM 1400D manufactured by Tokyo Seimitsu Co.,Ltd was used for the measurement. The cutoff wavelength used herein was2.5 mm. Then, aluminum was vacuum vapor deposited on this scatteringlayer-attached glass substrate to a thickness of 80 nm, the diffusereflectivity of a film formation surface of the aluminum layer wasmeasured, and the ratio of scattering light was calculated. LANBDA 950manufactured by Perkin Elmer Inc. was used for the measurement.

The results thereof are shown in Table 1.

TABLE 1 Surface Diffuse Ra Rλa Ra/Rλa Ares Reflection Glass Material(μm) (μm) (10⁻²) Ratio Ratio A Fired at 3.39 143 2.37 1.0352 98% 550° C.Fired at 2.58 216 1.19 1.0111 85% 560° C. Fired at 2.53 236 1.07 1.008883% 570° C. Fired at 1.68 302 0.556 1.0027 60% 580° C. B 4.74 492 0.9631.0082 72% C 0.04 171 0.0234 1.0001 38%

Here, A is glass materials comprising 23.1 mmol % of P₂O₅, 12.0 mol % ofB₂O₃, 11.6 mol % of Li₂O, 16.6 mol % of Bi₂O₃, 8.7 mol % of TiO₂, 17.6mol % of Nb₂O₅ and 10.4 mol % of WO₃ and fired at the respectivetemperatures, B is a glass material having the same composition as Awith exception that Bi₂O₃ is decreased to 5.5 mol % and that Na₂O andK₂O are added in amounts of 4 mol % and 2.5 mol %, respectively, andfired at 530° C., and C is a glass material having the composition shownin Table 12 and obtained by firing a scattering layer constituted. Theglass transition temperature Tg of A is 499° C., and that of B is 481°C.

By adjusting the firing conditions like this, the waviness can be givento the surface, and this makes it possible to reduce specularreflectivity. Accordingly, even when scatterability of the scatteringlayer is low, reflection due to the fact that the reflective electrodehas specularity can be decreased.

Further, the content of the above-mentioned scattering materials in theabove-mentioned scattering layer is desirably at least 1 vol %.

The experiment results reveals that when the scattering material iscontained in an amount of 1 vol % or more, sufficient lightscatterability can be obtained.

Furthermore, there are the case where the scattering material is pores,the case where it is material particles having a composition differentfrom that of the base layer and the case where it is precipitatedcrystals of the base layer. These may be used either alone or as amixture thereof.

When the scattering material is pores, the size of the pores, poredistribution or density can be adjusted by adjusting the firingconditions such as the firing temperature.

When the scattering material is material particles having a compositiondifferent from that of the base layer, the size, distribution or densityof the scattering material can be adjusted by adjusting the materialcomposition or the firing conditions such as the firing temperature.

When the above-mentioned scattering material is precipitated crystals ofthe glass constituting the above-mentioned base layer, the size of thepores, pore distribution or density can be adjusted by adjusting thefiring conditions such as the firing temperature.

Further, the first refractive index of the base layer for at least onewavelength of wavelengths λ(430 nm<λ<650 nm) is desirably 1.8 or more.Although it is difficult to form a high refractive index material layer,it becomes easy to adjust the refractive index by adjusting the materialcomposition of the glass material.

The respective members will be described in detail below.

<Substrate>

As substrate 101 used for the formation of the translucent substrate, amaterial having a high refractive index for visible light is used,mainly such as a glass substrate. As the material having a highrefractive index, specifically, a plastic substrate as well as the glasssubstrate may be used. As a material for the glass substrate, aninorganic glass such as alkali glass, non-alkali glass or quartz glassmay be mentioned. Further, as a material for the plastic substrate, apolyester, a polycarbonate, a polyether, a polysulfone, apolyethersulfone, a polyvinyl alcohol or a fluorine-containing polymersuch as polyvinylidene fluoride or polyvinyl fluoride may be mentioned.Incidentally, in order to prevent moisture from passing through thesubstrate, the plastic substrate may be constituted so that barrierproperties are given thereto. The thickness of the translucent substrate101 is preferably from 0.1 mm to 2.0 mm in the case of glass. However,too thin substrate results in a decrease in strength, so that it isparticularly preferred that the thickness is from 0.5 mm to 1.0 mm.

Incidentally, in order to prepare the scattering layer by glass frit,the thermal expansion coefficient is preferably 50×10⁻⁷/° C. or more,more preferably 70×10⁻⁷/° C. or more and still more preferably 80×10⁻⁷/°C. or more, because a problem of strain and the like are encountered.

Further, it is desirable that the average thermal expansion coefficientof the scattering layer at 100° C. to 400° C. is from 70×10⁻⁷(° C.⁻¹) to95×10⁻⁷(° C.⁻¹), and that the glass transition temperature is from 450°C. to 550° C.

Scattering Layer

A constitution, a preparation method and characteristics of thescattering layer and a measuring method of the refractive index will bedescribed in detail below. Incidentally, in order to realize animprovement of the light-extraction efficiency which is the principalobject of the invention, the refractive index of the scattering layermust be equivalent to or higher than the refractive index of atranslucent electrode material, although details thereof are describedlater.

Calculating Method

In order to obtain characteristics of the scattering layer describedlater, the present inventors performed optical simulations, andexamined, for respective parameters, influences exerted on theextraction efficiency thereby. A computing software used is a softwareSPEOS manufactured by OPTIS Corporation. This software is a ray tracesoftware, and at the same time, it is possible to apply a theoreticalformula of Mie scattering to the scattering layer. The thickness of theorganic layer actually used as a layer having a light-emitting function,such as a charge-injection-transport layer or a light-emitting layer, isactually from about 0.1 μm to about 0.3 μm in total. However, in the raytrace, the angle of ray does not change even when the thickness ischanged. Accordingly, it was taken as 1 μm of the minimum thicknessallowed in the software. For a similar reason, the total thickness ofthe glass substrate and the scattering layer was taken as 100 μm.Further, for simplicity, calculation was made dividing the organic layerand the translucent electrode into three of the charge-injection layerand the light-emitting layer, a hole-injection-transport layer, and thetranslucent electrode. In the calculation, the refractive indexes ofthese are assumed as the same. However, the refractive indexes of theorganic layer and the translucent electrode are equivalent values, sothat the calculated results are not largely changed. Strictlyconsidered, a waveguide mode caused by interference stands, because theorganic layer is thin. However, the results are not largely changed,even when geometric-optically treated. This is therefore sufficient forestimating the advantages of this invention. In the organic layer,emitted light is assumed to be outgone from a total of 6 faces withouthaving directivity. The calculation was made, taking the total lightflux amount as 1,000 lm and the number of light rays as 100,000 rays or1,000,000 rays. The light outgone from the translucent substrate wascaptured by a receiving surface mounted 10 μm above the translucentsubstrate, and the extraction efficiency was calculated from theilluminance thereof.

Constitution

In this embodiment, as described above, the scattering layer 102 isformed by forming a glass powder on the glass substrate by a method suchas coating and firing it at a desired temperature, and has the basematerial 102 having a first refractive index and a plurality ofscattering materials 104 dispersed in the above-mentioned base material102 and having a second refractive index different from that of theabove-mentioned base material. The intralayer distribution of theabove-mentioned scattering materials in the above-mentioned scatteringlayer decreases from the inside of the above-mentioned scattering layerto the outermost surface. Use of the glass layer makes it possible tokeep smoothness of the surface while having excellent scatteringcharacteristics, as described above, and use thereof on the lightoutgoing surface side of the light-emitting device or the like makes itpossible to realize extremely high-efficient light extraction.

Further, as the scattering layer, a material (base material) having amain surface coated and having a high light transmittance may be used.As the base material, a glass, a crystallized glass, a translucent resinor a translucent ceramic may be used. As a material for the glass, aninorganic glass such as soda lime glass, borosilicate glass, non-alkaliglass or quartz glass may be used. Incidentally, the plurality ofscattering materials 104 (for example, pores, precipitated crystals,material particles different from the base material or phase-separatedglass) are formed in the inside of the base material. The particle asused herein means a small solid material, and there is a filler or aceramic. Further, the pore means an air or gas material. Furthermore,the phase-separated glass means a glass composed of two or more kinds ofglass phases. Incidentally, when the scattering material is the pore,the size of the scattering material indicates a diameter of a void.

Further, in order to realize an improvement of the light-extractionefficiency which is the principal object of the invention, therefractive index of the scattering layer must be equivalent to or higherthan the refractive index of the translucent electrode material. Whenthe refractive index is low, a loss cue to total reflection occurs at aninterface between the base material and the translucent electrodematerial. The refractive index of the base material is only required toexceed for at least one portion (for example, red, blue, green or thelike) in the emission spectrum range of the scattering layer. However,it exceeds preferably over the whole region (430 nm to 650 nm) of theemission spectrum range, and more preferably over the whole region (360nm to 830 nm) of the wavelength range of visible light.

Further, in order to prevent the interelectrode short circuit of theorganic LED element, the main surface of the scattering layer isrequired to be smooth. For that purpose, it is unfavorable that thescattering materials protrude from the main surface of the scatteringlayer. Also in order to prevent the scattering materials from protrudingfrom the main surface of the scattering layer, it is preferred that thescattering materials are not present within 0.2 μm from the main surfaceof the scattering layer. The arithmetic average roughness (Ra) of themain surface of the scattering layer specified in JIS B0601-1994 ispreferably 30 nm or less, more preferably 10 nm or less (see Table 1),and particularly desirably 1 nm or less. Although both the refractiveindexes of the scattering material and the base material may be high,the difference (Δn) in the refractive indexes is preferably 0.2 or morefor at least one portion in the emission spectrum range of thescattering layer. In order to obtain sufficient scatteringcharacteristics, the difference (Δn) in the refractive indexes is morepreferably 0.2 or more over the whole region (430 nm to 650 μm) of theemission spectrum range or the whole region (360 nm to 830 μm) of thewavelength range of visible light.

In order to obtain the maximum refractive index difference, aconstitution of using a high refractive index glass as theabove-mentioned high light transmittance material and the gas material,namely the pores, as the scattering material is desirable. In this case,the refractive index of the base material is desirably as high aspossible, so that the high refractive index glass is preferably used asthe base material. For components of the high refractive index glass,there can be used the high refractive index glass containing one or twoor more kinds of components selected from P₂O₅, SiO₂, B₂O₃, Ge₂O andTeO₂ as network formers, and one or two or more kinds of componentsselected from TiO₂, Nb₂O₅, WO₃, Bi₂O₃, La₂O₃, Gd₂O₃, Y₂O₃, ZrO₂, ZnO,BaO, PbO and Sb₂O₃ as high refractive index components. In addition, ina sense of adjusting characteristics of the glass, an alkali oxide, analkaline earth oxide, a fluoride or the like may be used within therange not impairing characteristics required for the refractive index.Specific glass systems include a B₃O₃—ZnO—La₂O₃ system, aP₂O₅—B₂O₃—R′₂O—R″O—TiO₂—Nb₂O₅—WO₃—Bi₂O₃ system, a TeO₂—ZnO system, aB₂O₃—Bi₂O₃ system, a SiO₂—Bi₂O₃ system, a SiO₂—ZnO system, a B₂O₃—ZnOsystem, a P₂O₅—ZnO system and the like, wherein R′ represents an alkalimetal element, and R″ represents an alkaline earth metal element.Incidentally, the above are examples, and the glass system is notconstrued as being limited to these examples as long as it isconstituted so as to satisfy the above-mentioned conditions.

It is also possible to change color of light emission by allowing thebase material to have a specific transmittance spectrum. As colorants,known ones such as a transition metal oxide, a rare-earth metal oxideand a metal colloid can be used alone or in combination thereof.

Here, in general, white light emission is necessary for backlight andlighting applications. For whitening, there are known a method in whichred, blue and green area spatially selectively coated (selective coatingmethod), a method of laminating light-emitting layers having differentlight emission colors (lamination method) and a method of color changinglight emitted in blue with a color changing material spatiallyseparately provided (color changing method). In the backlight andlighting applications, what is necessary is just to uniformly obtainwhite color, so that the lamination method is generally used. Thelight-emitting layers to be laminated are used in such a combinationthat white color is obtained by additive color mixing. For example, ablue-green layer and an orange layer are laminated, or red, blue andgreen are laminated, in some cases. In particular, in the lightingapplication, color reproducibility at a reflective surface is important,so that it is desirable to have an emission spectrum necessary for avisible light region. When the blue-green layer and the orange layer arelaminated, lighting of one with a high proportion of green deterioratescolor reproducibility, because of low light emission intensity of greencolor. The lamination method has a merit that it is unnecessary tospatially change a color arrangement, whereas it has the following twoproblems. The first problem is that the emitted light extracted isinfluenced by interference, because the film thickness of the organiclayer is thin as described above. Accordingly, color changes dependingon the viewing angle. In the case of white color, such a phenomenonbecomes a problem in some cases, because the sensitivity of the humaneye to color is high. The second problem is that a carrier balance isdisrupted during light emission to cause changes in light-emittingluminance in each color, resulting in changes in color.

A conventional organic LED element has no idea of dispersing afluorescent material in a scattering layer or a diffusing layer, so thatit can not solve the above-mentioned problem of changes in color.Accordingly, the conventional organic LED element has been insufficientyet for the backlight and lighting applications. However, in thesubstrate for an organic LED element and the organic LED element of theinvention, the fluorescent material can be used in the scatteringmaterial or the base material. This can cause an effect of performingwavelength conversion by light emission from the organic layer to changecolor. In this case, it is possible to decrease the light emissioncolors of the organic LED, and the emitted light is extracted afterbeing scattered. Accordingly, the angular dependency of color andchanges in color with time can be inhibited.

Preparation Method of Scattering Layer

The preparation of the scattering layer is carried out by coating andfiring. In particular, from the viewpoint of forming rapidly anduniformly a film thickness of 10 to 100 μm with a large area, a methodof preparing the layer by using a frit-pasted glass is preferred. Inorder to utilize a frit paste method, it is desirable that the softeningpoint (Ts) of the glass of the scattering layer is lower than the strainpoint (SP) of the substrate glass, and that the difference in thethermal expansion coefficient (α) is small, for inhibiting thermaldeformation of the substrate glass. The difference between the softeningpoint and the strain point is preferably 30° C. or more, and morepreferably 50° C. or more. Further, the difference in the expansioncoefficient between the scattering layer and the substrate glass ispreferably ±10×10⁻⁷ (1/K) or less, and more preferably ±5×10⁻⁷ (1/K) orless. The frit paste as used herein indicates one in which a glasspowder is dispersed in a resin, a solvent, a filler or the like. Glasslayer coating becomes possible by patterning the frit paste using apattern forming technique such as screen printing and firing it. Thetechnical outline will be described below.

Frit Paste Material

1. Glass Powder

The particle size of the glass powder is from 1 μm to 10 μm. In order tocontrol the thermal expansion of the film fired, a filler isincorporated in some cases. As the filler, specifically, zircon, silica,alumina or the like may be used, and the particle size thereof is from0.1 μm to 20 μm.

Glass materials will be described below.

In the invention, the above-mentioned scattering layer uses a glasscontaining 20 to 30 mol % of P₂O₅, 3 to 14 mol % of B₂O₃, 10 to 20 mol %of Li₂O, Na₂O and K₂O in terms of total amount thereof, 10 to 20 mol %of Bi₂O₃, 3 to 15 mol % of TiO₂, 10 to 20 mol % of Nb₂O₅ and 5 to 15 mol% of WO₃, wherein the total amount of the above-mentioned components is90 mol % or more.

The glass composition for forming the scattering layer is notparticularly limited, as long as desired scattering characteristics areobtained and it can be frit-pasted and fired. However, in order tomaximize the extraction efficiency, examples thereof include a systemcontaining P₂O₅ as an essential component and further one or morecomponents of Nb₂O₅, Bi₂O₃, TiO₂ and WO₃; a system containing B₂O₃, ZnOand La₂O₃ as essential components and one or more components of Nb₂O₅,ZrO₂, Ta₂O₅ and WO₃; a system containing SiO₂ as an essential componentand one or more components of Nb₂O₅ and TiO₂; a system containing Bi₂O₃as a main component and SiO₂, B₂O₃ and the like as network formingcomponents, and the like.

Incidentally, in all glass systems used as the scattering layer in theinvention, As₂O₃, PbO, CdO, ThO₂ and HgO which are components havingadverse effects on the environment are not contained, except for thecase of inevitable contamination therewith as impurities derived fromraw materials.

The scattering layer containing P₂O₅ and one or more components ofNb₂O₅, Bi₂O₃, TiO₂ and WO₃ is preferably a glass within the compositionrange of 15 to 30% of P₂O₅, 0 to 15% of SiO₂, 0 to 18% of B₂O₃, 5 to 40%of Nb₂O₅, 0 to 15% of TiO₂, 0 to 50% of WO₃, 0 to 30% of Bi₂O₃, providedthat Nb₂O₅+TiO₂+WO₃+Bi₂O₃ is from 20 to 60%, 0 to 20% of Li₂O, 0 to 20%of Na₂O, 0 to 20% of K₂O, provided that Li₂O+Na₂O+K₂O is from 5 to 40%,0 to 10% of MgO, 0 to 10% of CaO, 0 to 10% of SrO, 0 to 20% of BaO, 0 to20% of ZnO and 0 to 10% of Ta₂O₅, in terms of mol %.

Effects of the respective components are as follows in terms of mol %.

P₂O₅ is an essential component forming a skeleton of this glass systemand performing vitrification. However, when the content is too small,devitrification of the glass increases to result in failure to obtainthe glass. Accordingly, it is preferably 15% or more, and morepreferably 18% or more. On the other hand, when the content is toolarge, the refractive index decreases to result in failure to achievethe object of the invention. Accordingly, it is preferably 30% or less,and more preferably 28% or less.

B₂O₃ is an optional component as a component which is added into theglass, thereby improving resistance to devitrification and decreasingthe thermal expansion coefficient. When the content is too large, therefractive index decreases. It is therefore preferably 18% or less, andmore preferably 15% or less.

SiO₂ is an optional component as a component which is added in slightamounts, thereby stabilizing the glass and improving resistance todevitrification. When the content is too large, the refractive indexdecreases. It is therefore preferably 15% or less, and more preferably10% or less.

Nb₂O₅ is an essential component improving the refractive index and alsohaving an effect of enhancing weather resistance at the same time.Accordingly, the content is preferably 5% or more, and more preferably8% or more. On the other hand, when the content is too large,devitrification increases to result in failure to obtain the glass.Accordingly, the content thereof is preferably 40% or less, and morepreferably 35% or less.

TiO₂ is an optional component improving the refractive index. However,when the content is too large, coloring of the glass increases to causean increased loss in the scattering layer, resulting in failure toachieve the object of improving the light-extraction efficiency.Accordingly, the content is preferably 15% or less, and more preferably13% or less.

WO₃ is an optional component improving the refractive index anddecreasing the glass transition temperature to decrease the firingtemperature. However, excessive introduction thereof results in coloringof the glass to cause a decrease in the light-extraction efficiency.Accordingly, the content thereof is preferably 50% or less, and morepreferably 45% or less.

Bi₂O₃ is a component improving the refractive index, and can beintroduced into the glass in relatively large amounts while keepingstability of the glass. However, excessive introduction thereof poses aproblem that the glass is colored to decrease the transmittance.Accordingly, the content is preferably 30% or less, and more preferably25% or less.

In order to increase the refractive index more than the desired value,one or more components of Nb₂O₅, TiO₂, WO₃ and Bi₂O₃ described abovemust be necessarily contained. Specifically, the total amount of(Nb₂O₅+TiO₂+WO₃+Bi₂O₃) is preferably 20% or more, and more preferably25% or more. On the other hand, when the total amount of thesecomponents is too large, coloring occurs, or devitrification excessivelyincreases. It is therefore preferably 60% or less, and more preferably55% or less.

Ta₂O₅ is an optional component improving the refractive index. However,when the amount added is too large, resistance to devitrificationdecreases. In addition to this, it is expensive. Accordingly, thecontent thereof is preferably 10% or less, and more preferably 5% orless.

The alkali metal oxides (R₂O) such as Li₂O, Na₂O and K₂O has an effectof improving meltability to decrease the glass transition temperatureand concurrently an effect of enhancing affinity with the glasssubstrate to increase adhesion. For this reason, it is desirable tocontain one or two or more kinds of these. These are containedpreferably in an amount of 5% or more, and more preferably in an amountof 10% or more, as the total amount of (Li₂O+Na₂O+K₂O). However, whenthey are excessively contained, stability of the glass is impaired. Inaddition to this, all are components decreasing the refractive index, sothat the refractive index of the glass decreases, resulting in failureto the desired improvement of the light-extraction efficiency.Accordingly, the total content is preferably 40% or less, and morepreferably 35% or less.

Li₂O is a component for decreasing the glass transition temperature andimproving solubility. However, when the content is too much,devitrification excessively increases to result in failure to obtainhomogeneous glass. Further, the thermal expansion coefficientexcessively increases to increase the difference in the expansioncoefficient from the substrate. At the same time, the refractive indexalso decreases to result in failure to achieve a desired improvement ofthe light-extraction efficiency. Accordingly, the content is desirably20% or less, and more preferably 15% or less.

Both of Na₂O and K₂O are optional components improving meltability.However, excessive inclusion thereof causes a decrease in the refractiveindex, resulting in failure to achieve the desired light-extractionefficiency. Accordingly, the contents are each preferably 20% or less,and more preferably 15% or less.

ZnO is a component improving the refractive index and decreasing theglass transition temperature. However, when it is excessively added,devitrification of the glass increases to result in failure to obtainthe homogeneous glass. Accordingly, the content is preferably 20% orless, and more preferably 18% or less.

BaO is a component improving the refractive index and concurrentlyimproving solubility. However, when it is excessively added, stabilityof the glass is impaired. Accordingly, the content thereof is preferably20% or less, and more preferably 18% or less.

MgO, CaO and SrO are optional components improving solubility, andcomponents decreasing the refractive index at the same time.Accordingly, the contents are each preferably 10% or less, and morepreferably 8% or less.

In order to obtain the high refractive index and stable glass, the totalamount of the above-mentioned components is preferably 90% or more, morepreferably 93% or more, and still more preferably 95% or more.

In addition to the components described above, a refining agent, avitrification enhancing component, a refractive index adjustingcomponent, a wavelength converting component or the like may be added insmall amounts within the range not impairing necessary glasscharacteristics. Specifically, the refining agents include Sb₂O₃ andSnO₂, the vitrification enhancing components include GeO₂, Ga₂O₃ andIn₂O₃, the refractive index adjusting components include ZrO₂, Y₂O₃,La₂O₃, Gd₂O₃ and Yb₂O₃, and the wavelength converting components includerare-earth components such as CeO₂, Eu₂O₃ and Er₂O₃, and the like.

The scattering layer containing B₂O₃ and La₂O₃ as essential componentsand one or more components of Nb₂O₅, ZrO₂, Ta₂O₅ and WO₃ is preferably aglass within the composition range of: 20 to 60% of B₂O₃, 0 to 20% ofSiO₂, 0 to 20% of Li₂O, 0 to 10% of Na₂O, 0 to 10% of K₂O, 5 to 50% ofZnO, 5 to 25% of La₂O₃, 0 to 25% of Gd₂O₃, 0 to 20% of Y₂O₃, 0 to 20% ofYb₂O₃, provided that La₂O₃+Gd₂O₃+Y₂O₃+Yb₂O₃ is from 5 to 30%, 0 to 15%of ZrO₂, 0 to 20% of Ta₂O₅, 0 to 20% of Nb₂O₅, 0 to 20% of WO₃, 0 to 20%of Bi₂O₃ and 0 to 20% of BaO, in terms of mol %.

Effects of the respective components are as follows in terms of mol %.

B₂O₃ is a network forming oxide, and an essential component in thisglass system. When the content is too small, glass formation is notperformed, or resistance to devitrification of the glass decreases.Accordingly, it is contained preferably in an amount of 20% or more, andmore preferably in an amount of 25% or more. On the other hand, when thecontent is too large, the refractive index decreases, and further,resistance decreases. Accordingly, the content is restricted to 60% orless, and more preferably, it is 55% or less.

SiO₂ is a component improving stability of the glass when added into theglass of this system. However, when the amount introduced is too large,the refractive index decreases, and the glass transition temperatureincreases. For this reason, the content is preferably 20% or less, andmore preferably 18% or less.

Li₂O is a component decreasing the glass transition temperature.However, when the amount introduced is too large, resistance todevitrification of the glass decreases. For this reason, the content ispreferably 20% or less, and more preferably 18% or less.

Na₂O and K₂O improve solubility. However, introduction thereof causes adecrease in resistance to devitrification and a decrease in therefractive index. Accordingly, each content is preferably 10% or less,and more preferably 8% or less.

ZnO is an essential component improving the refractive index of theglass and decreasing the glass transition temperature. For this reason,the amount introduced is preferably 5% or more, and more preferably 7%or more. On the other hand, when the amount added is too large,resistance to devitrification decreases to result in failure to obtainthe homogeneous glass. Accordingly, it is preferably 50% or less, andmore preferably 45% or less.

La₂O₃ is an essential component achieving a high refractive index andimproving weather resistance when introduced into the B₂O₃ system glass.For this reason, the amount introduced is preferably 5% or more, andmore preferably 7% or more. On the other hand, when the additive amountis too large, the glass transition temperature increases, or resistanceto devitrification of the glass decreases, resulting in failure toobtain the homogeneous glass. Accordingly, the content is preferably 25%or less, and more preferably 22% or less.

Gd₂O₃ is a component achieving a high refractive index, improvingweather resistance when introduced into the B₂O₃ system glass andimproving stability of the glass by coexistence with La₂O₃. However,when the amount introduced is too large, stability of the glassdecreases. Accordingly, the content thereof is preferably 25% or less,and more preferably 22% or less.

Y₂O₃ and Yb₂O₃ are components achieving a high refractive index,improving weather resistance when introduced into the B₂O₃ system glassand improving stability of the glass by coexistence with La₂O₃. However,when the amount introduced is too large, stability of the glassdecreases. Accordingly, the contents are each preferably 20% or less,and more preferably 18% or less.

The rare-earth oxides such as La₂O₃, Gd₂O; Y₂O₃ and Yb₂O₃ are componentsessential for achieving a high refractive index and improving weatherresistance of the glass. Accordingly, the total amount of thesecomponents, La₂O₃+Gd₂O₃+Y₂O₃+Yb₂O₃, is preferably 5% or more, and morepreferably 8% or more. However, when the amount introduced is too large,resistance to devitrification of the glass decreases to result infailure to obtain the homogeneous glass. Accordingly, it is preferably30% or less, and more preferably 25% or less.

ZrO₂ is a component for improving the refractive index. However, whenthe content is too large, resistance to devitrification decreases, orthe liquid-phase temperature is excessively increased. Accordingly, thecontent is preferably 15% or less, and more preferably 10% or less.

Ta₂O₅ is a component for improving the refractive index. However, whenthe content is too large, resistance to devitrification decreases, orthe liquid-phase temperature is excessively increased. Accordingly, thecontent is preferably 20% or less, and more preferably 15% or less.

Nb₂O₅ is a component for improving the refractive index. However, whenthe content is too large, resistance to devitrification decreases, orthe liquid-phase temperature is excessively increased. Accordingly, thecontent is preferably 20% or less, and more preferably 15% or less.

WO₃ is a component for improving the refractive index. However, when thecontent is too large, resistance to devitrification decreases, or theliquid-phase temperature is excessively increased. Accordingly, thecontent is preferably 20% or less, and more preferably 15% or less.

Bi₂O₃ is a component for improving the refractive index. However, whenthe content is too large, resistance to devitrification decreases, orcoloring occurs in the glass to cause a decrease in the refractiveindex, resulting in a decrease in extraction efficiency. Accordingly,the content is preferably 20% or less, and more preferably 15% or less.

BaO is a component for improving the refractive index. However, when thecontent is too large, resistance to devitrification decreases.Accordingly, it is preferably 20% or less, and more preferably 15% orless.

In order to conform to the object of the invention, the total amount ofthe above-mentioned components is desirably 90% or more, and morepreferably 95% or more. Even a component other than the above-mentionedcomponents, it may be added for the purposes of refining or animprovement of solubility, as long as it does not deviate from theefficiency of the present invention Such components include, forexample, Sb₂O₃, SnO₂, MgO, CaO, SrO, GeO₂, Ga₂O₃, In₂O₃ and fluorine.

The scattering layer containing SiO₂ as an (essential component and oneor more components of Nb₂O₅, TiO₂ and Bi₂O₃ is preferably a glass withinthe composition range of: 20 to 50% of SiO₂, 0 to 20 of B₂O₃, 1 to 20%of Nb₂O₅, 1 to 20% of TiO₂, 0 to 15% of Bi₂O₃, 0 to 15% of ZrO₂,provided that Nb₂O₅+TiO₂+Bi₂O₃+ZrO₂ is from 5 to 40%, 0 to 40% of Li₂O,0 to 30% of Na₂O, 0 to 30% of K₂O, provided that Li₂O+Na₂O+K₂O is from 1to 40%, 0 to 20% of MgO, 0 to 20% of CaO, 0 to 20% of SrO, 0 to 20% ofBaO and 0 to 20% of ZnO, in terms of mol %.

SiO₂ is an essential component acting as a network former for formingthe glass. When the content thereof is too small, no glass is formed.Accordingly, it is preferably 20% or more, and more preferably 22% ormore.

B₂O₃ is added in relatively small amounts with SiO₂, thereby assistingglass formation and decreasing devitrification. However, when thecontent is too large, the refractive index decreases. Accordingly, thecontent thereof is preferably 20% or less, and more preferably 18% orless.

Nb₂O₅ is an essential component for improving the refractive index, andthe content thereof is preferably 1% or more, and more preferably 3% ormore. However, excessive addition thereof causes a decrease inresistance to devitrification of the glass to result in failure toobtain the homogeneous glass. Accordingly, the content thereof isdesirably 20% or less, and more preferably 18% or less.

TiO₂ is an essential component for improving the refractive index, andthe content thereof is preferably 1% or more, and more preferably 3% ormore. However, excessive addition thereof causes a decrease inresistance to devitrification of the glass to result in failure toobtain the homogeneous glass and causes coloring to increase a loss dueto absorption at the time when light propagates in the scattering layer.For this reason, the content thereof is desirably 20% or less, and morepreferably 18% or less.

Bi₂O₃ is an component for improving the refractive index. However,excessive addition thereof causes a decrease in resistance todevitrification of the glass to result in failure to obtain thehomogeneous glass and causes coloring to increase a loss due toabsorption at the time when light propagates in the scattering layer.For this reason, the content thereof is desirably 15% or less, and morepreferably 12% or less.

ZrO₂ is a component improving the refractive index without deterioratingthe degree of coloring. However, when the content is too large,resistance to devitrification of the glass decreases to result infailure to obtain the homogeneous glass. For this reason, the content ispreferably 15%, or less, and more preferably 10% or less.

In order to obtain the high refractive index glass,Nb₂O₅+TiO₂+Bi₂O₃+ZrO₂ is preferably 5% or more, and more preferably 8%or more. On the other hand, when this total amount is too large,resistance to devitrification of the glass decreases, or coloringoccurs. Accordingly, it is preferably 40% or less, and more preferably38% or less.

Li₂O, Na₂O and K₂O are components improving solubility, decreasing theglass transition temperature and enhancing affinity with the glasssubstrate. For this reason, the total amount of these components,Li₂O+Na₂O+K₂O, is preferably 1% or more, and more preferably 3% or more.On the other hand, when the content of the alkali oxide component is toolarge, resistance to devitrification of the glass decreases to result infailure to obtain the homogeneous glass. Accordingly, the contentthereof is preferably 40% or less, and more preferably 35% or less.

BaO is a component improving the refractive index and improvingsolubility at the same time. However, when it is excessively contained,stability of the glass is impaired to result in failure to obtain thehomogeneous glass. Accordingly, the content thereof is preferably 20% orless, and more preferably 15% or less.

MgO, CaO, SrO and ZnO are components improving solubility of the glass,and moderate addition thereof can decrease resistance to devitrificationof the glass. However, when they are excessively contained,devitrification increases to result in failure to obtain the homogeneousglass. Accordingly, the contents thereof are each preferably 20% orless, and more preferably 15% or less.

In order to conform to the object of the invention, the total amount ofthe above-mentioned components is desirably 90% or more. Further, even acomponent other than the above-mentioned components may be added for thepurposes of refining, an improvement of solubility and the like withinthe range not impairing the advantages of the invention. Such componentsinclude, for example, Sb₂O₃, SnO₂, GeO₂, Ga₂O₃, In₂O₃, WO₃, Ta₂O₅,La₂O₃, Gd₂O₃, Y₂O₃ and Yb₂O.

The scattering layer containing Bi₂O₃ as a main component and SiO₂, B₂O₃and the like as glass forming auxiliaries is preferably a glass withinthe composition range of: 10 to 50% of Bi₂O₃, 1 to 40 of B₂O₃, 0 to 30%of SiO₂, provided that B₂O₃+SiO₂ is from 10 to 40%, 0 to 20% of P₂O₅, 0to 15% of Li₂O, 0 to 15% of Na₂O, 0 to 15% of K₂O, 0 to 20% of TiO₂, 0to 20% of Nb₂O₅, 0 to 20% of TeO₂, 0 to 10% of MgO, 0 to 10% of CaO, 0to 10% of SrO, 0 to 10% of BaO, 0 to 10% of GeO₂ and 0 to 10% of Ga₂O₃,in terms of mol %.

Effects of the respective components are as follows in terms of mol %.

Bi₂O₃ is an essential component achieving a high refractive index andstably forming the glass even when introduced in large amounts. For thisreason, the content thereof is preferably 10% or more, and morepreferably 15% or more. On the other hand, excessive addition thereofcauses coloring in the glass to absorb light which should originallytransmit, resulting in a decrease in extraction efficiency. In additionto this, devitrification increases to result in failure to obtain thehomogeneous glass. Accordingly, the content thereof is preferably 50% orless, and more preferably 45% or less.

B₂O₃ is an essential component acting as a network former in the glasscontaining Bi₂O₃ in large amounts to assist glass formation, and thecontent thereof is preferably 1% or more, and more preferably 3% ormore. However, when the amount added is too large, the refractive indexof the glass decreases. Accordingly, it is preferably 40% or less, andmore preferably 38% or less.

SiO₂ is a component acting to assist Bi₂O₃ in glass formation as anetwork former. However, when the content is too large, the refractiveindex decreases. Accordingly, it is preferably 30% or less, and morepreferably 25% or less.

B₂O₃ and SiO₂ improve glass formation by a combination thereof, so thatthe total amount thereof is preferably 5% or more, and more preferably10% or more. On the other hand, when the amount introduced is too large,the refractive index decreases. Accordingly, it is preferably 40% orless, and more preferably 38% or less.

P₂O₅ is a component assisting glass formation and inhibitingdeterioration of the degree of coloring. However, when the content istoo large, the refractive index decreases. Accordingly, it is preferably20% or less, and more preferably 18% or less.

Li₂O, Na₂O and K₂O are components for improving glass solubility andfurther decreasing the glass transition temperature. However, when theyare excessively contained, devitrification increases to result infailure to obtain the homogeneous glass. Accordingly, the contentsthereof are each preferably 15% or less, and more preferably 13% orless. Further, when the total amount of the above alkali oxidecomponents, Li₂O+Na₂O+K₂O, is too large, the refractive index decreases,and further, resistance to devitrification decreases. Accordingly, it ispreferably 30% or less, and more preferably 25% or less.

TiO₂ is a component improving the refractive index. However, when thecontent is too large, coloring occurs, or resistance to devitrificationdecreases, resulting in failure to obtain the homogeneous glass.Accordingly, the content is preferably 20% or less, and more preferably18% or less.

Nb₂O₅ is a component improving the refractive index. However, when theamount introduced is too large, resistance to devitrification of theglass decreases to result in failure to obtain the homogeneous glass.For this reason, the content is preferably 20% or less, and morepreferably 18% or less.

TeO₂ is a component improving the refractive index without deterioratingthe degree of coloring. However, excessive introduction thereof resultsin a decrease in resistance to devitrification, which causes coloring atthe time when fired after fritting. Accordingly, the content thereof ispreferably 20% or less, and more preferably 15% or less.

GeO₂ is a component improving stability of the glass while keeping therefractive index relatively high. However, it is extremely expensive, sothat the content is preferably 10% or less, and more preferably 8% orless. It is still more preferred not to contain it.

Ge₂O₃ is a component improving stability of the glass while keeping therefractive index relatively high. However, it is extremely expensive, sothat the content is preferably 10% or less, and more preferably 8% orless. It is still more preferred not to contain it.

In order to conform to the object of the invention, the total amount ofthe above-mentioned components is desirably 90% or more, and morepreferably 95% or more. Even a component other than the above-mentionedcomponents may be added for the purposes of refining, an improvement ofsolubility, adjustment of the refractive index, and the like within therange not impairing the advantages of the invention. Such componentsinclude, for example, Sb₂O₃, SnO₂, In₂O₃, ZrO₂, Ta₂O₅, WO₃, La₂O₃,Gd₂O₃, Y₂O₃, Yb₂O₃ and Al₂O₃.

The glass composition for forming the scattering layer is notparticularly limited, as long as desired scattering characteristics areobtained and it can be frit-pasted and fired. However, in order tomaximize the extraction efficiency, examples thereof include a systemcontaining P₂O₅ and one or more components of Nb₂O₅, Bi₂O₃, TiO₂ andWO₃; a system containing B₂O₃ and La₂O₃ as essential components and oneor more components of Nb₂O₅, ZrO₂, Ta₂O₅ and WO₃; a system containingSiO₂ as an essential component and one or more components of Nb₂O₅ andTiO₂; a system containing Bi₂O₃ as a main component and SiO₂, B₂O₃ andthe like as glass forming auxiliaries, and the like. Incidentally, inall glass systems used as the scattering layer in the invention, As₂O₃,PbO, CdO, ThO₂ and HgO which are components having adverse effects onthe environment should not be contained, except for the case ofinevitable contamination therewith as impurities derived from rawmaterials.

In the composition containing P₂O₅ and one or more components of Nb₂O₅,Bi₂O₃, TiO₂ and WO₃, a glass within the following composition range ispreferred. Incidentally, the following composition is represented by mol%.

2. Resin

The resin supports the glass powder and the filler after screenprinting. As a specific example, there is used ethyl cellulose,nitrocellulose, an acrylic resin, vinyl acetate resin, a butyral resin,a melamine resin, an alkyd resin, a rosin resin or the like. Used asbase resins are ethyl cellulose and nitrocellulose. Incidentally, abutyral resin, a melamine resin, an alkyd resin and a rosin resin areused as additives for improving coated film strength. The debinderizingtemperature at the time of firing is from 350° C. to 400° C. for ethylcellulose, and from 200° C. to 300° C. for nitrocellulose.

3. Solvent

The solvent dissolves the resin and adjusts the viscosity necessary forprinting. Further, it does not dry during printing, and rapidly dries ina drying process. One having a boiling point of 200° C. to 230° C. isdesirable. For adjustment of the viscosity, the solid content ratio andthe drying rate, a mixture of some solvents is used. Specific examplesinclude ether type solvents (butyl carbitol (BC), butyl carbitol acetate(BCA), diethylene glycol di-n-butyl ether, dipropylene glycol dibutylether, tripropylene glycol butyl ether and butyl cellosolve acetate),alcohol type solvents (α-terpineol, pine oil and Dowanol), ester typesolvents (2,2,4-trimethyl-1,3-pentanediol monoisobutyrate) and phthalicacid ester type solvents (DBP (dibutyl phthalate), DMP (dimethylphthalate) and DOP (dioctyl phthalate)). Mainly used are α-terpineol and2,2,4-trimethyl-1,3-pentanediol monoisobutyrate. Incidentally, DBP(dibutyl phthalate), DMP (dimethyl phthalate) and DOP (dioctylphthalate) also function as a plasticizer.

4. Others

A surfactant may be used for viscosity adjustment and frit dispersionpromotion. A silane coupling agent may be used for frit surfacemodification.

Preparation Method of Frit Paste

(1) Frit Paste

A glass powder and a vehicle are prepared. The vehicle as used hereinmeans a mixture of a resin, a solvent and a surfactant. Specifically, itis obtained by putting the resin, the surfactant and the like in thesolvent heated at 50° C. to 80° C., and then, allowing the resultingmixture to stand for about 4 hours to about 12 hours, followed byfiltering.

Then, the glass powder and the vehicle are mixed by a planetary mixer,and then, uniformly dispersed by a three-roll mill. Thereafter, theresulting mixture is kneaded by a kneader. Usually, the vehicle is usedin an amount of 20 to 30 wt % based on 70 to 80 wt % of the glassmaterial.

As the glass powder used herein, one having a particle size D₁₀ of 0.2μm or more and D₉₀ of 5 μm or less is desirably used. When D₉₀ of theparticle size exceeds 5 μm, the value to the film thickness of thescattering layer increases to result in a tendency to decrease filmthickness uniformity. On the other hand, when D₁₀ of the particle sizeis less than 0.2 μm, the interface existence ratio increases, whichposes a problem that crystals are easily precipitated to cause easydevitrification.

(2) Printing

The frit paste prepared in (1) is printed by using a screen printer. Thefilm thickness of a frit paste film formed can be controlled by the meshroughness of a screen plate, the thickness of an emulsion, the pressingforce in printing, the squeegee pressing amount and the like. Afterprinting, drying is performed in a firing furnace.

(3) Firing

A substrate printed and dried is fired in the firing furnace. The firingcomprises debinderizing treatment for decomposing the resin in the fritpaste and allowing it to disappear and firing treatment for sinteringand softening the glass powder. The debinderizing temperature is from350° C. to 400° C. for ethyl cellulose, and from 200° C. to 300° C. fornitrocellulose. Heating is carried out in the atmosphere for 30 minuteto 1 hour. Then, the temperature is raised to sinter and soften theglass. The firing temperature is from the softening temperature to thesoftening temperature +20° C., and the shape and size of pores remainingin the inside vary depending on the treatment temperature. Then, coolingis carried out to form a glass layer on the substrate. Although thethickness of the film obtained is from 5 μm to 30 μm, a thicker glasslayer can be formed by lamination printing.

Incidentally, when a doctor blade printing method or a die coat printingmethod is used in the above-mentioned printing process, it becomespossible to form a thicker film (green sheet printing). A film is formedon a PET film or the like, and dried, thereby forming a green sheet.Then, the green sheet is heat pressed on the substrate by a roller orthe like, and a fired film is obtained through a firing proceduresimilar to that of the frit paste. The thickness of the resulting filmis from 50 μm to 400 μm. However, it is possible to form a thicker glassfilm by using the green sheets laminated.

Density of Scattering Material in Scattering Layer and Size ofScattering Material

FIG. 11 is a graph showing the relationship between the light-extractionefficiency (%) and the content (vol %) of a scattering material. In thefollowing, for simplicity, calculation was made dividing the organiclayer and the translucent electrode into three parts, theelectron-injection-transport layer and the light-emitting layer, thehole-injection-transport layer, and the translucent electrode. Here, inthe above-mentioned graph, calculation was made for theelection-injection-transport layer (thickness: 1 μm, refractive index:1.9), the light-emitting layer (thickness: 1 μm, refractive index: 1.9),the hole-injection-transport layer (thickness: 1 μm, refractive index:1.9), the scattering layer (thickness: 30 μm, the refractive index ofthe base material: 1.9, the refractive index of the scattering material:1.0), the translucent electrode (thickness: 100 μm, refractive index:1.54) and the light flux 1,000 lm divided into 100,000 rays (wavelength:550 nm). As shown in the graph, the content of the scattering materialin the scattering layer is preferably 1 vol % or more. Although thebehavior varies depending on the size of the scattering material, whenthe content of the scattering material in the scattering layer is 1 vol%, the light-extraction efficiency can be 40% or more. Further, when thecontent of the scattering material in the scattering layer is 5 vol % ormore, the light-extraction efficiency can be 65% or more. This istherefore more preferred. Furthermore, when the content of thescattering material in the scattering layer is 10 vol % or more, thelight-extraction efficiency can be improved to 70% or more. This istherefore still more preferred. In addition, when the content of thescattering material in the scattering layer is approximately 15 vol %,the light-extraction efficiency can be improved to 80% or more. This istherefore particularly preferred. Incidentally, in view of massproduction of the scattering layers, the content is preferably from 10vol % to 15 vol % at which it is difficult to be affected by productionvariations.

Incidentally, the graph also shows the relationship between the size ofthe scattering material and the light-extraction efficiency.Specifically, in the case where the size of the scattering material is 1μm, the light-extraction efficiency can be 70% or more, even when thecontent of the scattering material is within the range of 1 vol % to 20vol %. In particular, when the content of the scattering material iswithin the range of 2 vol % to 15 vol %, the light-extraction efficiencycan be 80% or more. Further, in the case where the size of thescattering material is 2 μm, the light-extraction efficiency can be 65%or more, even when the content of the scattering material is within therange of 1 vol % to 20 vol %. In particular, when the content of thescattering material is 5 vol % or more, the light-extraction efficiencycan be 80% or more. Furthermore, in the case where the size of thescattering material is 3 μm, the light-extraction efficiency can be 60%or more, even when the content of the scattering material is within therange of 1 vol % to 20 vol %. In particular, when the content of thescattering material is 5 vol % or more, the light-extraction efficiencycan be 80% or more. In addition, in the case where the size of thescattering material is 5 μm, the light-extraction efficiency can be 50%or more, even when the content of the scattering material is within therange of 1 vol % to 20 vol %. In particular, when the content of thescattering material is 10 vol % or more, the light-extraction efficiencycan be 80% or more. Further, in the case where the size of thescattering material is 7 μm, the light-extraction efficiency can be 45%or more, even when the content of the scattering material is within therange of 1 vol % to 20 vol %. In particular, when the content of thescattering material is 10 vol % or more, the light-extraction efficiencycan be 80% or more. Furthermore, in the case where the size of thescattering material is 10 μm, the light-extraction efficiency can be 40%or more, even when the content of the scattering material is within therange of 1 vol % to 20 vol %. In particular, when the content of thescattering material is 15 vol % or more, the light-extraction efficiencycan be 80% or more. The above shows that when the size of the scatteringmaterial is large, the efficiency is improved with an increase in thecontent. On the other hand, it is seen that when the size of thescattering material is small, the light-extraction efficiency isimproved, even in the case where the content is small.

Refractive Index of Scattering Material

FIG. 12 is a graph showing the relationship between the light-extractionefficiency (%) and the refractive index of a scattering material. In thefollowing, for simplicity, calculation was made dividing the organiclayer and the translucent electrode into three parts, theelectron-injection-transport layer and the light-emitting layer, thehole-injection-transport layer, and the translucent electrode. Here, inthe above-mentioned graph, calculation was made for theelection-injection-transport layer (thickness: 1 μm, refractive index:1.9), the light-emitting layer (thickness: 1 μm, refractive index: 1.9),the hole-injection-transport layer (thickness: 1 μm, refractive index:1.9), the scattering layer (thickness: 30 μm, the refractive index ofthe base material: 2.0, the size of the scattering material: 2 μm, thenumber of the scattering materials: about 36,000,000, the content of thescattering material: 15 vol %), the translucent electrode (thickness:100 μm, refractive index: 1.54) and the light flux 1,000 lm divided into100,000 rays (wavelength: 550 nm). As shown in the graph, when thedifference between refractive index (2.0) of the base material and therefractive index of the scattering material is 0.2 or more (therefractive index of the scattering material is 1.8 or less), thelight-extraction efficiency can be 80% % or more. This is thereforeparticularly preferred. Incidentally, even when the difference betweenrefractive index of the base material and the refractive index of thescattering material is 0.1 (the refractive index of the scatteringmaterial is 1.9), the light-extraction efficiency can be 65% or more.

Thickness of Scattering Layer

FIG. 13 is a graph showing the relationship between the light-extractionefficiency (%) and the content (vol %) of a scattering, material. In thefollowing, for simplicity, calculation was made dividing the organiclayer and the translucent electrode into three parts, theelectron-injection-transport layer and the light-emitting layer, thehole-injection-transport layer, and the translucent electrode. Here, inthe above-mentioned graph, calculation was made for theelectron-injection-transport layer (thickness: 1 μm, refractive index:1.9), the light-emitting layer (thickness: 1 μm, refractive index: 1.9),the hole-injection-transport layer (thickness: 1 μm, refractive index:1.9), the scattering layer (the refractive index of the base material:2.0, the size of the scattering material: 2 μm, the refractive index ofthe scattering material: 1.0), the translucent electrode (thickness: 100μm, refractive index: 1.54) and the light flux 1,000 lm divided into100,000 rays (wavelength: 550 nm). As shown in the graph, in the casewhere the content of the scattering material in the scattering layer is1 vol % or more, the light-extraction efficiency can be 55% or more,even when the thickness of the scattering layer is 15 μm or less. Thisis therefore preferred. Further, in the case where the content of thescattering material in the scattering layer is from 5 vol % to 15 vol %,the light-extraction efficiency can be 80% or more, even when thethickness of the scattering layer is 15 μm or less, or 60 μm or more.This is therefore particularly preferred.

Number of Scattering Materials

FIG. 14 is a graph showing the relationship between the light-extractionefficiency (%) and the number (number/mm²) of scattering material(particles). In the following, for simplicity, calculation was madedividing the organic layer and the translucent electrode into threeparts, the electron-injection-transport layer and the light-emittinglayer, the hole-injection-transport layer, and the translucentelectrode. Here, in the above-mentioned graph, calculation was made forthe electron-injection-transport layer (thickness: 1 μm, refractiveindex: 1.9), the light-emitting layer (thickness: 1 μm, refractiveindex: 1.9), the hole-injection-transport layer (thickness: 1 μm,refractive index: 1.9), the scattering layer (the refractive index ofthe base material: 2.0, the size of the scattering material: 2 μm, therefractive index of the scattering material: 1.0), the translucentelectrode (thickness: 100 μm, refractive index: 1.54) and the light flux1,000 lm divided into 100,000 rays (wavelength: 550 nm). As shown in thegraph, it is seen that the light-extraction efficiency varies dependingon the number of the scattering materials, regardless of the thicknessof the scattering layer. As shown in the graph, when the number of thescattering materials per 1 mm² of the scattering layer is 1×10⁴ or more,the light-extraction efficiency can be 55% or more. This is thereforepreferred. Further, when the number of the scattering materials per 1mm² of the scattering layer is 2.5×10⁵ or more, the light-extractionefficiency can be 75% or more. This is therefore more preferred.Furthermore, when the number of the scattering materials per 1 mm² ofthe scattering layer is from 5×10⁵ to 2×10⁶, the light-extractionefficiency can be 80% or more. This is therefore particularly preferred.Here, even when the size of the scattering material is 60 μm or more andthe number of the scattering materials is 3×10⁶, the light-extractionefficiency can be 70% or more.

Transmittance of Base Material of Scattering Layer

FIG. 15 is a graph showing the relationship between the light-extractionefficiency (%) and the transmittance at 1 mmt % of a base material ofthe scattering layer. In the following, for simplicity, calculation wasmade dividing the organic layer and the translucent electrode into threeparts, the electron-injection-transport layer and the light-emittinglayer, the hole-injection-transport layer, and the translucentelectrode. Here, in the above-mentioned graph, calculation was made forthe electron-injection-transport layer (thickness: 1 μm, refractiveindex: 1.9), the light-emitting layer (thickness: 1 μm, refractiveindex: 1.9), the hole-injection-transport layer (thickness: 1 μm,refractive index: 1.9), the scattering layer (thickness: 30 μm, therefractive index of the base material: 2.0, the size of the scatteringmaterial: 2 μm, the refractive index of the scattering material: 1.0,the number of the scattering materials: about 36,000,000, the content ofthe scattering material: 15 vol %), the translucent electrode(thickness: 100 μm, refractive index: 1.54) and the light flux 1,000 lmdivided into 100,000 rays (wavelength: 550 nm). As shown in the graph,even when the transmittance of the base material of the scattering layeris 50%, the light-extraction efficiency can be 55% or more. Further,when the transmittance of the base material of the scattering layer is90%, the light-extraction efficiency can be 80% or more. When a glass isused as the base material, the transmittance thereof is about 98%.Accordingly, the light-extraction efficiency can exceed 80%.

Reflectivity of Cathode

FIG. 16 is a graph showing the relationship between the light-extractionefficiency (%) and the reflectivity (%) of a cathode. In the following,for simplicity, calculation was made dividing the organic layer and thetranslucent electrode into three parts, the electron-injection-transportlayer and the light-emitting layer, the hole-injection-transport layer,and the translucent electrode. Here, in the above-mentioned graph,calculation was made for the electron-injection-transport layer(thickness: 1 μm, refractive index: 1.9), the light-emitting layer(thickness: 1 μm, refractive index: 1.9), the hole-injection-transportlayer (thickness: 1 μm, refractive index: 1.9), the scattering layer(thickness: 30 μm, the refractive index of the base material: 2.0, thesize of the scattering material: 2 μm, the refractive index of thescattering material: 1.0, the number of the scattering materials: about36,000,000, the content of the scattering material: 15 vol %), thetranslucent electrode (thickness: 100 μm, refractive index: 1.54) andthe light flux 1,000 lm divided into 100,000 rays (wavelength: 550 nm).As shown in the graph, when the reflectivity of the cathode decreases,the light-extraction efficiency also decreases. Here, the cathodereflectivity of a blue LED is from 80% to 90%, so that it is seen thatthe light-extraction efficiency of 40% to 50% is obtained. Here, thereflectivity of the organic LED element of patent document 1 is assumedto be 100%, and the light-extraction efficiency thereof is about 50%. Onthe other hand, when the reflectivity of the organic LED element of theinvention is taken as 100% and the same conditions as in thereflectivity of the organic LED element of patent document 1 areapplied, the light-extraction efficiency thereof exceeds 80%, as seenfrom the graph. Namely, it is seen that the light-extraction efficiency,of the organic LED element of the invention is 1.6 times better than thelight-extraction efficiency of the organic LED element of patentdocument 1. Accordingly, the organic LED of the invention can be used asa light source for lighting in place of a fluorescent lamp.

Refractive Indexes of Scattering Layer and Anode

FIG. 17 is a graph showing the relationship between the ratio of lightoutgoing to the scattering layer and the refractive index of the basematerial of the scattering layer. In the following, for simplicity,calculation was made dividing the organic layer and the translucentelectrode into three parts, the electron-injection-transport layer andthe light-emitting layer, the hole-injection-transport layer, and thetranslucent electrode. Here, in the above-mentioned graph, calculationwas made for the electron-injection-transport layer (thickness: 1 μm,refractive index: 1.9), the light-emitting layer (thickness: 1 μm,refractive index: 1.9), the hole-injection-transport layer (thickness: 1μm, refractive index: 1.9), the scattering layer (thickness: 30 μm, thesize of the scattering material: 2 μm, the refractive index of thescattering material: 1.0, the number of the scattering materials: about36,000,000, the content of the scattering material: 15 vol %), thetranslucent electrode (thickness: 100 μm, refractive index: 1.54) andthe light flux 1,000 lm divided into 100,000 rays (wavelength: 550 nm).As shown in the graph, when the refractive index of an anode is largerthan the refractive index of the scattering layer, total reflectionoccurs on a surface of the scattering layer to decrease the amount oflight entering the scattering layer. Accordingly, it is seen that thelight-extraction efficiency decreases. It is therefore preferred thatthe refractive index of the scattering layer of the invention isequivalent to or higher than the refractive index of the anode.

Relationship between Refractive Index of Base Material of ScatteringLayer and White Emitted Light Color

FIG. 18 is a graph showing the relationship between the wavelength andthe refractive index of the base material of the scattering layer. FIG.19 is the results showing the relationship between the wavelength andthe illuminance of a light receiving surface. Incidentally, FIG. 19 (a)is a spectral diagram corresponding to Case 1 of FIG. 18, FIG. 19 (b) isa spectral diagram corresponding to Case 2 of FIG. 18, FIG. 19 (c) is aspectral diagram corresponding to Case 3 of FIG. 18, and FIG. 19 (d) isa spectral diagram corresponding to Case 4 of FIG. 18. In the following,for simplicity, calculation was made dividing the organic layer and thetranslucent electrode into three parts, the electron-injection-transportlayer and the light-emitting layer, the hole-injection-transport layer,and the translucent electrode. Here, in the above-mentioned graphs,calculation was made for the electron-injection-transport layer(thickness: 1 μm, refractive index: 1.9), the light-emitting layer(thickness: 1 μm, refractive index: 1.9), the hole-injection-transportlayer (thickness: 1 μm, refractive index: 1.9), the scattering layer(thickness: 30 μm, the refractive index of the base material, the sizeof the scattering material: 2 μm, the refractive index of the scatteringmaterial: 1.0, the number of the scattering materials: about 36,000,000,the content of the scattering material: 15 vol %), the translucentelectrode (thickness: 100 μm, refractive index: 1.54) and the light flux1,000 lm divided into 100,000 rays. Incidentally, the refractive indexof the translucent electrode was taken as 1.9. As shown in FIG. 19, whenthe refractive index of the base material of the scattering layer islower than the refractive indexes of the organic layer and thetranslucent electrode, it is seen that the extraction efficiency at thatwavelength decreases to result in changes in color. To describe itconcretely, as known from FIG. 19 (c), in the case where the wavelengthis 550 nm or more, it is seen that the light-emitting efficiencydecreases when the refractive index becomes 1.9 or less. Namely, rednessof the organic LED element deteriorates. In this case, it becomesnecessary to form the element in which redness is strengthened.

Measuring Methods of Refractive Index of Scattering Layer

There are the following two methods for measuring the refractive indexof the scattering layer. One is a method of analyzing composition of thescattering layer, thereafter preparing a glass having the samecomposition, and evaluating the refractive index by a prism method. Theother is a method of polishing the scattering layer as thin as 1 to 2μm, and performing ellipsometry measurement in a region of about 10 μmin diameter having no pores to evaluate the refractive index.Incidentally, in the invention, it is assumed that the refractive indexis evaluated by the prism method.

Surface Roughness of Scattering Layer

The scattering layer has a main surface on which the translucentelectrode is provided. As described above, the scattering layer of theinvention contains the scattering material. As described above, when thesize of the scattering material is large, even the smaller contentthereof can improve the light-extraction efficiency. However, accordingto experiments of the inventors, there is a tendency that the larger thesize is, the larger the arithmetic average roughness (Ra) of the mainsurface of the scattering layer becomes, when projected from the mainsurface of the scattering layer. As described above, the translucentelectrode is provided on the main surface of the scattering layer.Accordingly, there is a problem that the larger arithmetic averageroughness (Ra) of the main surface of the scattering layer causes ashort circuit between the translucent electrode and the scatteringlayer, resulting in no light emission of the organic EL element. Theabove-mentioned patent document 1 discloses, in paragraph 0010, that theunevenness formed on the substrate poses a problem even when it is aboutseveral microns. However, according to experiments by the inventors, ithas been proved that light emission of the organic EL element is notobtained in the case of several microns.

Translucent Electrode

The translucent electrode (anode) 103 is required to have a translucencyof 80% or more, in order to extract the light generated in the organiclayer 110 to the outside. Further, in order to inject many holes, onehaving a high work function is required. Specifically, there is used amaterial such as ITO (indium tin oxide), SnO₂, ZnO, IZO (indium zincoxide), AZO (ZnO—Al₂O₃: a zinc oxide doped with aluminum), GZO(ZnO—Ga₂O₃: a zinc oxide doped with gallium), Nb-doped TiO₂ or Ta-dopedTiO₂. The thickness of the anode 103 is preferably 100 nm or more.Incidentally, the refractive index of the anode 103 is from 1.9 to 2.2.Here, an increase in carrier concentration can decrease the refractiveindex of ITO. ITO is commercially available as a standard containing 10wt % of SnO₂. The refractive index of ITO can be decreased by increasingthe Sn concentration more than this. However, although the carrierconcentration is increased by an increase in the Sn concentration, themobility and transmittance are decreased. It is therefore necessary todetermine the Sn amount, achieving a balance of these. Incidentally, itgoes without saying that the translucent electrode may be used as thecathode.

Organic Layer (Layer Having Light-Emitting Function)

The organic layer 110 is a layer having a light-emitting function andcomprises a hole-injection layer 111, hole-transport layer 112, alight-emitting layer 113, an electron-transport layer 114 and anelectron-injection layer 115. The refractive index of the organic layer110 is from 1.7 to 1.8.

Hole-Injection Layer

As the hole-injection layer 111, one whose ionization potential is notso different from the anode 103 is required, in order to lower ahole-injection barrier. An improvement of charge-injection efficiencyfrom an electrode interface in the hole-injection layer 111 decreasesthe driving voltage of the element and increases charge-injectionefficiency thereof. There is widely used polyethylenedioxythiophenedoped with polystyrene sulfonic acid (PSS) (PEDOT:PSS), as a polymer,and copper phthalocyanine (CuPc) of the phthalocyanine family as alow-molecular substance.

Hole-Transport Layer

The hole-transport layer 112 plays a role to transport holes injectedfrom the hole-injection layer 111 to the light-emitting layer 133. Asthe hole-transport layer 112, there is used, specifically, atriphenylamine derivative,N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPD),N,N′-diphenyl-N,N′-bis[N-phenyl-N-(2-naphthyl)-4′-aminobiphenyl-4-yl]-1,1′-biphenyl-4,4′-diamine(NPTE), 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (HTM2),N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-diphenyl-4,4′-diamine (TPD)or the like. The thickness of the hole-transport layer 112 is preferablyfrom 10 nm to 150 nm. The thinner the thickness is, the lower thevoltage can be. However, it is particularly preferably from 10 nm to 150nm, in terms of a problem of the interelectrode short circuit.

Light-Emitting Layer

The light-emitting layer provides a field in which injected electronsand holes recombine with each other, and a material having highlight-emitting efficiency is used. To describe it in detail, alight-emitting host material and a doping material of a light-emittingdye used in the light-emitting layer 113 function as recombinationcenters of the holes and the electrons injected from the anode and thecathode. Further, doping of the host material in the light-emittinglayer with the light-emitting dye provides high light emittingefficiency, and converts the light-emitting wavelength. These arerequired to have a suitable energy level for charge injection, to beexcellent in chemical stability and heat resistance, and to form ahomogeneous amorphous film. Further, these are required to be excellentin the kind of emission color and color purity, and to have highlight-emitting efficiency. The organic light-emitting materials includeslow-molecular and polymer materials. Further, they are classified intofluorescent and phosphorescent materials according to the light-emittingmechanism. Specifically, the light-emitting layer 113 includes metalcomplexes of quinoline derivatives such as atris(8-quinolinolate)aluminum complex (Alq₃), bis(8-hydroxy)quinaldinealuminum phenoxide (Alq′₂OPh), bis(8-hydroxy)quinaldine aluminum2,5-dimethylphenoxide (BAlq), amono(2,2,6,6-tetra-methyl-3,5-heptanedionate)lithium complex (Liq), amono(8-quinolinolate)sodium complex (Naq), amono(2,2,6,6-tetramethyl-3,5-heptanedionate)lithium complex, amono(2,2,6,6-tetramethyl-3,5-heptanedionate)sodium complex and abis(8-quinolinolate)calcium complex (Caq₂), and fluorescent substancessuch as tetraphenylbutadiene, phenylquinacridone (QD), anthracene,perylene and coronene. As the host material, preferred is aquinolinolate complex, and particularly preferred is an aluminum complexhaving 8-quinolinol or a derivative thereof as a ligand.

Electron-Transport Layer

The electron-transport layer 114 plays a role to transport holesinjected from the electrode. As the electron-transport layer 114, thereis used, specifically, a quinolinol aluminum complex (Alq₃), anoxadiazole derivative (for example, 2,5-bis(1-naphthyl)-1,3,4-oxadiazole(BND), 2-(4-t-butyl-phenyl)-5-(4-biphenyl)-1,3,4-oxadiazole (PBD) or thelike), a triazole derivative, a bathophenanthroline derivative, a silolederivative or the like.

Electron-Injection Layer

As the electron-injection layer 115, one which increases electroninjection efficiency is required. Specifically, a layer doped with analkali metal such as lithium (Li) or cesium (Cs) is provided on acathode interface, as the electron-injection layer 115.

Reflective Electrode

As the reflective electrode (cathode) 120, a metal having a small workfunction or an alloy thereof may be used. Specifically, examples of thecathode 120 include an alkali metal, an alkaline earth metal, a metal ofgroup 3 in the periodic table. Of these, Aluminum (Al), magnesium (Mg),an alloy thereof or the like is preferably used. Further, as a cathode120, a co-vapor-deposited film of Al and MgAg, a laminated electrode inwhich Al is vapor-deposited on a thin vapor-deposited film of LiF orLi₂O, or the like may be used. Further, in system using a polymer, alaminate of calcium (Ca) or barium (Ba) and aluminum (Al), or the likemay be used as the cathode 120.

Incidentally, it goes without saying that the reflective electrode maybe used as the anode.

Process for Producing Translucent Electrode-Attached TranslucentSubstrate (Laminate for Organic LED Element)

The process for producing the translucent electrode-attached translucentsubstrate of the invention will be described below with reference to thedrawing. FIG. 20 is a flow chart showing a process for producing thetranslucent electrode-attached translucent substrate of the invention.The process for producing the translucent electrode-attached translucentsubstrate of the invention comprises the step of preparing a translucentsubstrate (step 1100), the step of forming on the translucent substratea scattering layer comprising a base material having a first refractiveindex at a wavelength of emitted light of an organic LED element and aplurality of scattering materials provided in the inside of the basematerial and having a refractive index different from that of the basematerial (step 1110), and the step of forming on the scattering layer atranslucent electrode having a second refractive index equal to or lowerthan the first refractive index (step 1120).

First, the translucent substrate is prepared (step 1100). Specifically,a glass substrate or a plastic substrate is used herein as thetranslucent substrate.

Then, there is prepared the scattering layer comprising the basematerial having a first refractive index at a wavelength of emittedlight of the organic LED element and the plurality of scatteringmaterials provided inside the base material and having a refractiveindex different from that of the base material. Then, the scatteringlayer prepared is formed on the translucent substrate (step 1110).

Then, on the scattering layer, the translucent electrode having a secondrefractive index equal to or lower than the first refractive index (step1120) is formed. To describe it concretely, an ITO film is formed on thesubstrate, and the ITO film is etched, thereby forming the translucentelectrode. The film formation of ITO can be uniformly performed over thewhole surface of the glass substrate by sputtering or vapor deposition.An ITO pattern is formed by photolithography and etching. This ITOpattern becomes the translucent electrode (anode). A phenol novolakresin is used as a resist, and exposure and development are conducted.The etching may be either wet etching or dry etching. For example,patterning of ITO can be performed by using a mixed aqueous solution ofhydrochloric acid and nitric acid. As a resist remover, there can beused, for example, monoethanolamine.

Process for Producing Organic LED Element

The process for producing the organic LED element of the invention willbe described below by using the drawing. FIG. 21 is a flow chart showinga process for producing the organic LED element of the invention. Theprocess for producing the organic LED element of the invention comprisesthe step of preparing a translucent substrate (step 1100), the step offorming on the translucent substrate a scattering layer comprising abase material having a first refractive index at a wavelength of emittedlight of an organic LED element and a plurality of scattering materialsprovided in the inside of the base material and having a refractiveindex different from that of the base material (step 1110), the step offorming on the scattering layer a translucent electrode having a secondrefractive index equal to or lower than the first refractive index (step1120), the step of forming an organic layer on the translucent electrode(step 1200) and the step of forming a reflective electrode on theorganic layer (step 1210).

After steps 1100 to 1120 have been performed, the organic layer isformed on the translucent electrode (step 1200). The organic layer isformed herein by a combination of a coating method and a vapordeposition method. For example, when some one or more of the organiclayers are formed by the coating method, the other layers are formed bythe vapor deposition method. When the layer is formed by the coatingmethod and the upper layer is formed thereon by the vapor depositionmethod, condensation, drying and curing are performed before the organiclayer is formed by the vapor deposition method. Further, the organiclayer may be formed by only the coating method or only the vapordeposition method.

Then, the reflective electrode is formed on the organic layer (step1210). To describe it concretely, a metal material such as aluminum isvapor-deposited on the organic layer, thereby forming the reflectiveelectrode.

Next, there will be described the step of producing an opposed substratefor sealing, in order to seal the organic EL light-emitting elementformed by the above-mentioned steps. First, a glass substrate differentfrom the element substrate is prepared. This glass substrate isprocessed to form a desiccant housing portion for housing a desiccant.The glass substrate is coated with a resist, and a part of the substrateis exposed by exposure and development to form the desiccant housingportion. This exposed portion is made thin by etching, thereby formingthe desiccant housing portion.

As shown in FIG. 22, the desiccant 1310 such as calcium oxide isdisposed in this desiccant housing portion 1300, and then, twosubstrates are laminated and adhered to each other. Incidentally, FIG.22 is a cross-sectional view schematically showing a constitution of anorganic EL display device. Specifically, a seal material 1330 is appliedto a surface of the opposed substrate 1320 on which the desiccanthousing portion 1300 is provided, by using a dispenser. As the sealmaterial 1330, there can be used, for example, an epoxy-based UV-curableresin. Further, the seal material 1330 is applied to the whole peripheryof a region facing to the organic LED element. The two substrates arealigned, allowed to face each other, and then, irradiated with UV lightto cure the seal material, thereby adhering the substrates to eachother. Thereafter, in order to more enhance the curing of the sealmaterial, for example, heat treatment is performed in a clean oven of80° C. for 1 hour. As a result of this, a space between the substratesin which the organic EL element is present is isolated from the outsideof the substrates by the seal material and the pair of substrates.Deterioration of the organic EL element due to water and the likeremaining in the sealed space or entering therein can be prevented bydisposing the desiccant 1310.

Light emission from the organic layer 110 is outgone in a direction ofthe arrow. An optical sheet 1340 is attached to a surface of thesubstrate 101 opposite to a surface on which the organic LED element isformed, namely, an outgoing surface. The optical sheet 1340 has apolarizing plate and a ¼ wavelength plate, and functions as anantireflective film. The light from the organic thin film layer isextracted to the side of the surface on which this optical sheet 1340 isprovided.

Unnecessary portions in the vicinity of the periphery of the substratesare cut and removed. A signal electrode driver is connected to anodewiring 1350, and a scanning electrode driver is connected to cathodeconnection wiring. At an end portion of the substrate, a terminalportion connected to each wiring is formed. Ananisotropically-conductive film (ACF) is attached to this terminalportion, and a TCP (tape carrier package) provided with a drivingcircuit is connected thereto. Specifically, the ACF is temporarilypressed on the terminal portion. Then, the TCP containing the drivingcircuit is securely pressed on the terminal portion. The driving circuitis mounted thereby. This organic EL display panel is attached to a boxto complete the organic EL display device. Although the above shows thecase of a dot matrix display element, character display may be used.This is not limited to the above-mentioned constitution depending on theelement specification.

Embodiment 2 Another Constitutional Example of Organic LED Element

Then, constitutions of the electrode-attached translucent substrate(laminate for an organic LED element) and the laminate for an organicLED element of embodiment 2 of the invention will be described belowwith reference to the drawings. Incidentally, the same referencenumerals are given to the same constituents as those in FIG. 1, anddescriptions thereof will be omitted. FIG. 23 is a cross-sectional viewshowing other structures of the laminate for an organic LED element andthe laminate for an organic LED element of the invention.

The other organic LED element of the invention is constituted by anelectrode-attached translucent substrate (laminate for an organic LEDelement) 1400, an organic layer 1410 and a reflective electrode 120. Theelectrode-attached translucent substrate 1400 is constituted by atranslucent substrate 101, a scattering layer 1401 and a translucentelectrode 103. The organic layer 1410 is constituted by ahole-injection-transport layer 1411, a light-emitting layer 1412 and anelectron-injection-transport layer 1413.

The light-emitting layer 113 of the organic LED element of FIG. 1 isconstituted by three layers herein. Any one of the three layers isformed so as to emit light of any one color of three light emissioncolors (red, green and blue). However, the light-emitting layer 1412 ofthe organic LED element of FIG. 23 can be constituted by one layeremitting only blue light by using a fluorescent emission material (forexample, a filler) emitting red light and green light is the pluralityof scattering materials 1420 provided in the inside of the scatteringlayer 1401. Namely, according to the other constitution of the organicLED element of the invention, a layer emitting light of any one color ofred, green and blue can be used as the light-emitting layer to achievean effect that the organic LED element can be downsized.

In the above-mentioned embodiments, descriptions have been made for theconstitution in which the organic layer is sandwiched between thetranslucent electrode and the reflective electrode. However, a bifaciallight emission type organic EL layer may be constituted by making bothelectrodes translucent.

Further, the translucent electrode-attached translucent substrate of theinvention is effective to increase the efficiency of optical devicessuch as various light-emitting devices such as inorganic EL elements andliquid crystals and light-receiving devices such as light quantitysensors and solar pores, without being limited to the organic ELelements.

EXAMPLES Experimental Proof of Effect of Scattering Layer

An experimental proof for showing that the scattering layer is effectivefor an improvement of the light-extraction efficiency will be describedbelow. Sample 1 is an example having the scattering layer of theinvention, and sample 2 is a comparative example having the scatteringlayer in the inside of which no scattering material is provided. Thecalculating method is the same as the calculating method of thescattering layer described above. The respective conditions and results(front extraction efficiency) are shown in Table 2 below.

TABLE 2 Sample 1 Sample 2 Electron-Injection-Transport Layer Thickness(μm) 1 1 Refractive Index 1.9 1.9 Light-Emitting Layer Thickness (μm) 11 Refractive Index 1.9 1.9 Hole-Injection-Transport Layer Thickness (μm)1 1 Refractive Index 1.9 1.9 Scattering Layer Base Material Thickness(μm) 30 30 Refractive Index 1.9 1.9 Transmittance (%) 100 100 ScatteringMaterial Size (μm) 5 — Refractive Index 1 — Number of Particles (@ 1mm²) 1527932.516 — Content (vol %) 10 — Transmittance (%) 100 — GlassSubstrate Thickness (μm) 100 — Refractive Index 1.54 — Light Flux Numberof Light Rays Extracted 811.1/1000 210.4/1000 from Front Face Number ofLight Rays Extracted 47.86/1000   125/1000 from Side Face FrontExtraction Efficiency (%) 81.11 21.04

The results of comparison of front extraction efficiency between theexample and the comparative example are shown in FIG. 24. FIGS. 24 (a)and 24 (b) are graphs showing the results of observation from the frontunder conditions of samples 1 and 2, respectively. As shown in FIG. 24,according to the electrode-attached translucent substrate (laminate foran organic LED element) and the organic LED element of the invention, itbecomes possible to improve the light-extracting efficiency which isabout 20% when untreated to about 80%.

The contents and results of evaluation experiments made for confirmingthat the electrode-attached translucent substrate of the inventionimproves the outside extraction efficiency will be described below withreference to the drawings.

First, an evaluation element shown in FIG. 25 and FIG. 26 was prepared.Here, FIG. 25 is a cross-sectional view taken along line A-A as seenfrom the direction C in FIG. 26, showing a structure of the evaluationelement. FIG. 26 is a top view of the evaluation element seen from thedirection B in FIG. 25. Incidentally, in FIG. 25, in order to clarifythe positional relationship between a glass substrate 1610 and ascattering layer 1620, only the glass substrate 1610 and the scatteringlayer 1620 are described.

The evaluation element has the glass substrate 1610, the scatteringlayer 1620, an ITO (indium tin oxide) film 1630, an Alq₃(tris(8-quinolinolate)aluminum complex) film 1640 and a Ag film 1650. Inorder to compare herein the difference in light extraction efficiency bythe presence or absence of the scattering layer, the evaluation elementwas divided into two parts, region 1600A having the scattering layer andregion 1600B having no scattering layer. In the evaluation element inregion 1600A having the scattering layer, the scattering layer 1620 isformed on the glass substrate 1610. In the evaluation element in region1600B having no scattering layer, the ITO film 1630 is formed on theglass substrate 1610.

As the glass substrate, there was used a glass substrate, PD200 (tradename) manufactured by Asahi Glass Co., Ltd. This glass has a strainpoint of 570° C. and a thermal expansion coefficient of 83×10⁻⁷ (1/°C.). The glass substrate having such a high strain point and a highthermal expansion coefficient is suitable when a glass frit paste isfired to form the scattering layer.

The scattering layer 1620 is formed by using a high refractive indexglass frit paste layer. Here, a glass having the composition shown inTable 3 was prepared as the scattering layer 1620. This glass has aglass transition temperature of 483° C., a yield point of 528° C. and athermal expansion coefficient of 83×10⁻⁷ (1/° C.). The refractive indexnF of this glass at the F line (486.13 nm) is 2.03558, the refractiveindex nd at the d line (587.56 nm) is 1.99810, and the refractive indexnC at the C line (656.27 mn) is 1.98344. The refractive index wasmeasured with a refractometer (manufactured by Kalnew Optical IndustrialCo., Ltd, trade name: KRP-2). The glass transition temperature (Tg) andthe yield point (At) were measured with a thermal analysis instrument(manufactured by Bruker, trade name: TD5000SA) by a thermal expansionmethod at a rate of temperature increase of 5° C./min.

TABLE 3 Mass % Mol % P₂O₅ 16.4 23.1 B₂O₃ 1.9 5.5 Li₂O 1.7 11.6 Na₂O 1.24.0 K₂O 1.2 2.5 Bi₂O₃ 38.6 16.6 TiO₂ 3.5 8.7 Nb₂O₅ 23.3 17.6 WO₃ 12.110.4

The scattering layer 1620 was formed by the following procedure. Apowder raw material was prepared so as to give the composition indicatedby the ratio of Table 3. The powder raw material prepared was dry milledin a ball mill made of alumina for 12 hours to prepare a glass powderhaving an average particle size (d50, particle size at an integratedvalue of 50%, unit: μm) of 1 to 3 μm. Then, 75 g of the resulting glasspowder was kneaded with 25 g of an organic vehicle (one in which about10% by mass of ethyl cellulose was dissolved in α-terpineol and thelike) to prepare a paste ink (glass paste). This glass paste wasuniformly printed on the above-mentioned glass substrate to filmthicknesses after firing of 15 μm, 30 μm, 60 μm and 120 μm. After dryingat 150° C. for 30 minutes, this was once returned to room temperature.Then, the temperature was raised to 450° C., taking 45 minutes, and heldat 450° C. for 10 hours. Thereafter, the temperature was raised to 550°C., taking 12 minutes, and held at 550° C. for 30 minutes. Then, thetemperature was lowered to room temperature, taking 3 hours, to form aglass layer on the glass substrate. For the scattering layer having afilm thickness of 120 μm, a surface thereof was polished to a filmthickness of 60 μm. In the glass film formed thereby, many pores werecontained, which caused the occurrence of scattering. On the other hand,on the outermost glass surface of the scattering layer, there was notobserved such local unevenness as causing an interelectrode shortcircuit of the organic EL element, such as openings of the pores,although waviness was observed.

FIG. 27 is graphs showing waviness of the surfaces of the scatteringlayers. FIG. 27(A) shows waviness of the surface of the scattering layerhaving a film thickness of 60 μm, and FIG. 27(B) shows waviness of thesurface of the scattering layer having a film thickness of 60 μmobtained by polishing the scattering layer having a film thickness of120 μm. FIG. 28 is a graph in which the angle of a waviness slope inFIG. 27(A) is calculated. In FIG. 27(A) and FIG. 27(B), the measurementwas made by using a surface roughness tester (manufactured by TokyoSeimitsu Co., Ltd, SURFCOM 1400D). The angle of the slope of thescattering layer caused by the waviness is up to about 27°. This angleis smaller than the taper angle (40 to 50°) of an edge portion of anopening insulating film used in a passive type organic LED panel. Thisis therefore considered not to disturb coverage of the organic layer,the metal layer and the like. Further, the cause of the waviness isconsidered to be that the glass particles are not classified inpreparing the frit to cause large particles to be contained, whereby thelarge particle portions remain as the waviness at the time of firing.Accordingly, the waviness can be avoided by decreasing and equalizingthe size of the particles. Incidentally, the measurement results oflocal roughness are shown in FIG. 29 is graphs showing of surfaces ofscattering layers. FIG. 29(A) is the case where the surface of thescattering layer is not polished, and FIG. 29(B) is the case where thesurface of the scattering layer is polished. The arithmetic averageroughness Ra of the surface of the non-polished scattering layer was31.0 nm, and the arithmetic average roughness Ra of the surface of thepolished scattering layer was 23.5 nm. As seen from FIG. 29, no localprotrusion is observed on the surface of the scattering layer, and themeasurement results of the surface of the non-polished scattering layer(FIG. 29(A)) shows an unevenness shape similar to that of themeasurement results of the surface of the mirror-polished scatteringlayer (FIG. 29(B)). This is because the scattering material is pores andno pores are present in the surface. When the scattering material ismixed with the organic material (when a resin is used as the basematerial, and solid particles are used as the scattering material), thescattering material is exposed on the surface in some cases. It istherefore necessary to prevent the short circuit of the organic LEDelement by smoothing the roughness of the scattering layer surface.

On the other hand, in the polished one, the smooth surface is formed.

The total light transmittance and haze value of each scatteringlayer-attached substrate were measured. As a measurement device, therewas used a haze meter HGM-2 manufactured by Suga Test Instruments Co.,Ltd. As a reference, there was measured an untreated plate of theabove-mentioned glass substrate PD200. The results measured are shown inTable 4.

TABLE 4 Thickness of Total Light Haze Value Scattering Layer (μm)Transmittance (%) (%) 15 97.9 66.3 30 85.1 72.5 60 83.1 76.1

As shown above, it is seen that scatterability increases with anincrease in the film thickness of the scattering layer.

The ITO film 1630 was formed on the scattering layer 1620 and the glasssubstrate 1610 on which the scattering layer 1620 was not formed, to afilm thickness of 150 nm by sputtering. The sputtering was performed atroom temperature. Ar was 99.5 SCCM, O₂ was 0.5 SCCM, the pressure was0.4-7 Pa, and the input electric power was 2.35 W/cm². Then, using avapor deposition apparatus, the Alq₃ film 1640 was formed on the ITOfilm 1630, and the Ag film 1650 as formed on the Alq₃ film 1640, to filmthicknesses of 200 nm and 70 nm, respectively. In this evaluation, UVlight was irradiated from the upper side of the Ag film 1650 to excitethe Alq₃ film 1640. When the film thickness of the Ag film 1650 isthick, the UV light does not pass through. When it is too thin,fluorescent light from the Alq₃ film 1640 passes through without beingreflected. In the case of UV light of 320 nm, about 25% thereof can passthrough by adjusting the film thickness of the Ag film 1650. On theother hand, it becomes possible to restrain the ratio of the fluorescentlight passing through the Ag film 1650 to 1% or less. The Alq₃ film 1640is excited by the UV light which enters from the side of the Ag film1650. However, in the side of the Alq₃ film 1640 close to the Ag film1650, light emitted to the side of the glass substrate 1610 and lightemitted to the side of the Ag film 1650 and reflected by Ag to proceedto the glass substrate side interfere with each other to be weakened,because the difference in light path is small, whereas the reflection byAg causes a phase deviation of approximately π. This problem could besolved by making the film thickness of the Alq₃ film 1640 as thick as200 nm, thereby being able to increase the light-emitting luminancemeasured.

Using the evaluation element prepared as described above, light-emittingcharacteristics were immediately evaluated. A method for measuring andevaluating the light-emitting luminance is shown in FIG. 21. As anexcitation light source, a mercury xenon lamp (trade name: Suncure202-LS) 2100 manufactured by Asahi Glass Co., Ltd. was used. Light fromthe light source contains visible components, so that these componentswere removed by using a visible light filter 2110. In front of theevaluation element 1600, a stainless steel aperture (15 mm×10 mm) 2120was disposed to form an UV beam. A part of the UV light which hasentered the evaluation element 1600 passes through the Ag film 1650 andexcites the Alq₃ film 1640 to generate fluorescence. The UV lightirradiated to the region 1600A having the scattering layer of theevaluation element 1600 and to the region 1600B having no scatteringlayer, and fluorescent luminance of each region was measured with aluminance meter 2140. As the luminance meter, a luminance meter (tradename: LS-110) manufactured by Konica Minolta Holdings Inc. was used, andUV light filter was disposed in front of the luminance meter.

Measurement points are shown using the drawing. FIG. 31 is a diagramcorresponding to FIG. 26. As shown in FIG. 31, the measurement pointsare 5 points of a center and four corners of an UV irradiation region intotal. In a portion not having the scattering layer 1620, the UVirradiation region and the fluorescent light emission region are thesame as with each other. However, when there is the scattering layer1620, the fluorescent light emission region can be classified into tworegions, a strong central light-emitting region 2210 corresponding tothe UV irradiation region and a peripheral light-emitting region 2220 onthe outer side thereof in which light emission becomes weak asapproaching the periphery. Examples of luminance distribution of thecentral light-emitting region 2210 and the peripheral light-emittingregion 2220 are shown in FIG. 32. The luminance at line D-D in FIG. 31was measured herein. As known from FIG. 32, it is seen that light can beextracted not only from the fluorescent light emission region (centrallight-emitting region 2210), but also from the periphery thereof, whenthere is the scattering layer. This is said to have an effect of highluminance, compared to the conventional organic LED element, when theorganic LED element of the invention is used in lighting.

FIG. 33 shows the average front luminance of five measurement points foreach scattering layer changed in thickness (15 μm, 30 μm, 60 μm and 60μm after polishing). As shown in the graph, it is seen that the frontluminance increases with an increase in the film thickness of thescattering layer. Further, the surface-polished article having ascattering layer film thickness of 60 μm has a luminance equivalent tothat of the non-polished one. From this fact, it is considered that anincrease in luminance is mainly caused by scattering by thepore-containing high refractive index glass layer of the invention, notby surface waviness.

Actually, there is the peripheral light-emitting region 2220. The lightextracted from the periphery decreases in luminance with distance fromthe central light-emitting region, and becomes approximately 0 at about8 mm from an edge of the central light-emitting region, as shown in FIG.32. When a product is considered to which the invention is applied, inthe case where the size of a light-emitting portion is sufficientlylarger than 8 mm, the light extracted from the peripheral light-emittingregion is also allowed to be considered as a light flux extracted. FIG.34 shows the luminance at the time when the five-point average value iscorrected by measuring the amount of light of the peripherallight-emitting region for each scattering layer changed in thickness (15μm, 30 μm, 60 μm and 60 μm after polishing). Specifically, the luminancedistribution of the peripheral light-emitting region is measured, andthe total light flux amount is calculated. The correction is made byadding a value of that value divided by the area of the centrallight-emitting region to the luminance of the central light-emittingregion. In the region having no scattering layer, it is seen that thefront luminance ratio to the region having the scattering layer moreincreases because of no presence of the peripheral light-emittingregion.

FIG. 35 shows the ratio of the front luminance in the region having noscattering layer and the region having the scattering layer of eachevaluation element. As shown in the graph, only the UV irradiationregion provides the front luminance of 1.7 to 2.0 times that in the caseof having no scattering layer by insertion of the scattering layer ofthe invention. When the peripheral light-emitting region is considered,it can be estimated to reach 2.2 to 2.5 times.

Then, fluorescence spectra of the region having the scattering layer(thickness: 30 μm) and the region having no scattering layer weremeasured with a fluorophotometer (trade name: F4500) manufactured byHitachi High-Technologies Corporation. The measurement results thereofare shown in FIG. 36. Further, one in which the spectrum intensity ofthe region having no scattering layer is doubled, and overwritten on thespectrum of the region having the scattering layer is shown in FIG. 37.As is apparent from FIG. 36 and FIG. 37, it is seen that the regionhaving the scattering layer is approximately the same as the regionhaving no scattering layer in shape, and about 2 times in light emissionintensity. As a result of this, in the organic LED element, the emissionspectrum is changed by the interference in the inside of the element tochange the luminance in some cases, but it can be said that there is noinfluence thereof herein.

Then, the directional dependency of light intensity was measured. Ameasuring method is the same as the measuring method shown in FIG. 30.The luminance was measured with changing the position of a luminancemeter, and the light intensity was calculated from the resulting value.The measurement results are shown in FIG. 28. FIG. 39 is a graph inwhich the data of FIG. 38 is normalized by the front light intensity. Asshown in the graph, it was confirmed that the directional dependency oflight intensity did not change independently of the presence or absenceof the scattering layer to show strong non-directivity. From this, itwas confirmed that the improvement of the light-extraction efficiency ofthe invention which was confirmed for the front luminance was alsosimilarly improved for the total light flux.

Then, the particle size distribution of pores in the scattering layerprepared this time was measured. When the thickness of the scatteringlayer is 15 μm, all pores in the scattering layer can be distinguishedunder a microscope. The pores in a field of view of 90.5 μm×68.1 μm weredistinguished and counted by image processing. The results ofmeasurement at arbitrary three places of the scattering layer are shownin Table 5.

TABLE 5 Number of Average Pore Number of Observing Site Pores ParticleSize (μm) Pores per 1 mm² #1 598 1.3 1.07 × 10⁵ #2 934 1.33 1.51 × 10⁵#3 1371 1.4 2.22 × 10⁵

Further, cell diameter distribution at measurement point #2 is shown inFIG. 40. As is apparent from Table 5 and FIG. 40, many pores had a porediameter of 2 μm or less, and the average diameter was from 1.3 to 1.4μm. Furthermore, the number of pores per 1 mm² of the scattering layerwas from 1.1×10⁵ to 2.2×10⁵. When proportional calculation is carriedout on the cases where the thickness of the scattering layer is 30 μmand 60 μm, using the above-mentioned measurement results (the thicknessof the scattering layer is 15 μm), the number of pores in the case wherethe thickness of the scattering layer is 30 μm is from 2.2×10⁵ to4.4×10⁵, and the number of pores in the case where the thickness of thescattering layer is 60 μm is from 4.4×10⁵ to 8.8×10⁵.

FIG. 41 is a graph comparing the measurement results in the present caseto the relationship between the number of pores per 1 mm² and thelight-extraction efficiency at the time when the pore diameter is 2 μm.When the measurement results of FIG. 41 are compared to the simulationresults of FIG. 14, it has been seen that the evaluation element showsresults similar to the simulation results. To describe it concretely,when the thickness of the scattering layer is 15 μm, the number of poresis insufficient, and the light-extraction efficiency is insufficient.When the thickness of the scattering layer is 60 μm, thelight-extraction efficiency is also in a saturated region.

FIG. 42 shows the refractive indexes of the glass for the scatteringlayer, the ITO film and the Alq₃ film used in the example. As therefractive index of the ITO film as used herein, the data of a similarfilm formed at room temperature was used. The light-emitting wavelengthof the Alq₃ film is from 430 nm to 670 nm, so that the magnitudecorrelation of the refractive index is the scattering layer glass>theITO film>the Alq₃ film, over this entire wavelength region. From this,it is considered that there is no loss of light due to propagation inthe inside of the ITO film or the Alq₃ film. Incidentally, as the causesof a loss of the light-extraction efficiency, the reflectivity of the Agfilm and adsorption of the Alq₃ film, ITO film, the scattering layerglass and the substrate glass are considered. When the refractiveindexes and extinction coefficients of Ag and Alq₃ at a light-emittingpeak wavelength are taken as (n1, k1) and (n2, k2), respectively, thereflectivity in a vertical direction at an interface between Ag and Alq₃becomes ((n1−n2)²+(k1−k2)²)/((n1+n2)²+(k1+k2)²). From this, thereflectivity becomes about 93%, because n1=0.129, k1=3.25, n2=1.728 andk2=0.0016. From the graph of “WITH SCATTERING LAYER” in FIG. 16, thelight-extraction efficiency at this time is about 60%, when there is noadditional loss. In the case of the scattering layer having a filmthickness of 60 μm, which was prepared this time, the total lighttransmittance is as low as 83%, so that a loss in the scattering layeris deduced to be also on a non-negligible level. Although the light pathlength in the scattering layer is unknown herein, supposing that it isabout 1 mm, the loss at an adsorption of 17% can be estimated to beabout 12%, from the above-mentioned simulation results. When theabove-mentioned reflection loss of the Ag film is multiplied by the lossin the scattering layer glass, the light-extraction efficiency becomes60%×(100−12) %=53%. When the light-extraction efficiency in the case ofno scattering layer is assumed to be 20%, the light-extractionefficiency of 53% is 2.65 times that of the untreated one, andapproximately agrees with 2.5 times in the case where the peripheraldiffusion light is also considered. In order to improve a decrease inlight-extraction efficiency due to the reflection loss of the Ag filmand the loss in the scattering layer glass, it is also conceivablyeffective to decrease the reflectivity of the glass substrate with theair, as well as to increase the reflectivity of the refractive electrodeor the transmittance of the glass scattering layer. Specifically, it ismentioned that an antireflective film is formed on the outermost surfaceof the glass substrate. As described above, use of the invention make itpossible to extract the light propagating in the organic layer or theinside of the translucent electrode to the outside.

Example 2 Experimental Proof of Flatness of Main Surface of ScatteringLayer

There will be described below an experimental proof for showing that aflat main surface (the arithmetic average roughness is 30 nm or less) ofthe scattering layer is effective, in order to improve thelight-extraction efficiency.

First, as the glass substrate, there was used the above-mentioned glasssubstrate PD200 manufactured by Asahi Glass Co., Ltd. The scatteringlayer was prepared as follows. First, a powder raw material was preparedso as to give the glass composition of Table 3, melted in an electricfurnace of 1,100° C., cast into a roll to obtain glass flakes. Thisglass has a glass transition temperature of 499° C., a yield point of545° C. and a thermal expansion coefficient of 74×10⁻⁷ (1/° C.) (theaverage value of 100 to 300° C.). The refractive index nF of this glassat the F line (486.13 nm) is 2.0448, the refractive index nd at the dline (587.56 nm) is 2.0065, and the refractive index nC at the C line(656.27 nm) is 1.9918. Methods for measuring the refractive index andthe glass transition point-yield point are the same as in theabove-mentioned example.

The flakes prepared were further pulverized in a planetary mill made ofzirconia for 2 hours, and passed through a sieve to prepare a powder.For the particle size distribution at this time, D₅₀ was 0.905 μm, D₁₀was 0.398 μm, and D₉₀ was 3.024 μm. Then, 20 g of the resulting glasspowder was kneaded with 7.6 g of an organic vehicle to prepare a glasspaste. This glass paste was uniformly printed on the above-mentionedglass substrate to a circular form having a diameter of 10 mm and a filmthickness after firing of 15 μm. After drying at 150° C. for 30 minutes,this was once returned to room temperature. Then, the temperature wasraised to 450° C., taking 45 minutes, and held at 450° C. for 30 minutesThereafter, the temperature was raised to 550° C., taking 12 minutes,and held at 550° C. for 30 minutes to perform firing. Then, thetemperature was lowered to room temperature, taking 3 hours, to form ascattering layer on the glass substrate. In addition to this, scatteringlayers were also prepared at the same temperature profile as describedabove with the exception that only the holding-firing temperature waschanged to 570° C. and 580° C.

Then, the surface roughness of these was measured. For the measurement,there was used a three-dimensional noncontact surface profile measuringsystem, Micromap, manufactured by Ryoka Systems Inc. The measurement wasmade in two places in the vicinity of a central portion of the circularscattering layer, and a measuring area was a square with sides each 30μm long. Further, the cutoff wavelength of waviness was 10 μm. When theunevenness has a period of 10 μm or more, it is considered that a filmused for formation of the organic LED element, which is formed by asystem such as sputtering, vapor deposition, spin coating or spraying,can sufficiently follow that unevenness. For the unevenness having aperiod of less than 10 μm, it is considered that coatability thereofbecomes insufficient in vapor deposition and the like in some cases.FIG. 43 shows the arithmetic average roughness (Ra) of the scatteringlayers fired at the respective temperatures. One fired at 550° C. isincompletely fired, so that pores in the scattering layer are notspherical, and a surface thereof is roughened. Accordingly, when anelement is prepared thereon, a defect such as an interelectrode shortcircuit is liable to occur. Compared to this, in the layers fired at570° C. and 580° C., pores in the scattering layers become spherical,and surfaces thereof also become smooth.

TABLE 6 Mass % Mol % P₂O₅ 16.4 23.1 B₂O₃ 4.2 12 Li₂O 1.7 11.6 Na₂O 0 0K₂O 0 0 Bi₂O₃ 38.7 16.6 TiO₂ 3.5 8.7 Nb₂O₅ 23.4 17.6 WO₃ 12.1 10.4

The total light transmittance of the scattering layer-attached glasssubstrate thus produced was 77.8, and the haze value thereof was 85.2.As a measurement device, there was used a haze computer (trade name:HZ-2) manufactured by Suga Test Instruments Co., Ltd. As a reference,the measurement was made using an untreated plate of the glass substratePD200.

Then, the scattering layer-attached glass substrate produced asdescribed above and the glass substrate PD200 having no scattering layerwere each prepared, and an organic LED element was produced. First, anITO film was formed by mask film formation with a DC magnetron sputterto 150 nm as a transparent electrode. FIG. 44 shows the refractiveindexes of the glass for the scattering layer and ITO. Then, ultrasoniccleaning using pure water was performed, and thereafter, UV light wasirradiated with an excimer UV generator to clean a surface thereof.Then, α-NPD(N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4″-diamine was vapordeposited to 100 nm, Alq₃ (tris(8-hydroxyquinoline)aluminum to 60 nm,LiF to 0.5 nm, and Al to 80 nm, by using a vacuum vapor depositionapparatus. At this time, α-NPD and Alq₃ were deposited to a circularpattern having a diameter of 12 mm using a mask, and LiF and Al werepattern formed on the ITO pattern with the interposition of theabove-mentioned organic layers, using a mask having a region of 2 mmsquare, thereby completing an element.

Then, a concave portion was formed on PD200 as an opposed substrate bysand basting, and a photosensitive epoxy resin was applied forperipheral sealing to a bank around the concave portion. Then, theelement substrate and the opposed substrate were placed in a glove box,and a desiccant containing CaO was attached to the concave portion ofthe opposed substrate. Then, the element substrate and the opposedsubstrate were adhered to each other, followed by irradiation with UVlight to cure the resin for peripheral sealing. The state of theoccurrence of the interelectrode short circuit in each element is shownin Table 7. The self-healing as used herein means that a short-circuitportion is self-held by allowing an overcurrent of 10 mA to flow throughthe element to self-heal a short-circuit portion by the Joule heatthereof.

TABLE 7 State of Firing Interelectrode Temperature Short Circuit Remarks550° C. Δ to X A short circuit occurred at Ra of 52 nm. Self-healing wasimpossible. A short circuit occurred at Ra of 33 nm. Self-healing waspossible. 570° C. ◯ No short circuit occurred. 580° C. ◯ No shortcircuit occurred.

States in which the elements emit light are shown in FIG. 45 and FIG.46. Here, the element having the scattering layer is shown in FIG. 45,and the element having no scattering layer is shown in FIG. 46. In theelement having no scattering layer, light emission from only a region ofapproximately 2 mm square formed by the intersection of the ITO patternand the Al pattern is confirmed. However, in the element formed on thescattering layer, it is seen that the light is extracted not only fromthe above-mentioned region of approximately 2 mm square, but also from aperipheral scattering layer-forming portion to the atmosphere.

Thereafter, characteristics of the element in which the scattering layerwas fired at 570° C. were evaluated. For the measurement of the totallight flux, an EL characteristic measuring apparatus C9920-12manufactured by Hamamatsu Photonics K.K. was used. FIG. 47 shows thevoltage-current characteristic of the element having the scatteringlayer and the element having no scattering layer. As shown in the graph,an approximately similar characteristic is obtained. This shows that alarge leak current is not present even in the element formed on thescattering layer. Next, FIG. 48 shows the current-luminancecharacteristic. As shown in the graph, the light flux amount isproportional to the current independently of the presence or absence ofthe scattering layer. In the case of having the scattering layer, thelight flux amount increased 15%, compared to the case of having noscattering layer. This shows that the refractive index of the scatteringlayer is higher than the refractive index of ITO as the translucentelectrode at the light-emitting wavelength (450 nm to 700 nm) as shownin FIG. 44, so that EL emitted light of Alq₃ is inhibited from beingtotally reflected at an interface between ITO and the scattering layer,resulting in efficient extraction of light to the atmosphere.

Then, the angular dependency of color was evaluated. For opticalmeasurement, a multichannel spectroscope (trade name: C10027)manufactured by Hamamatsu Photonics K.K. was used. The measurement wasmade while rotating the element to the spectroscope, thereby measuringthe angular dependency of light-emitting luminance and light-emittingcolor. For the definition of the angle, the angle between a normal linedirection of the element and a direction extending from the element tothe spectroscope was defined as the measurement angle θ[°] (FIG. 49).Namely, a state in which the spectroscope is placed in front to theelement becomes 0°.

The spectrum data obtained are shown in FIGS. 50, 51, 52 and 53. FIG. 50shows the measurement results of the organic LED element having noscattering layer. FIG. 51 shows spectral data further normalized, takingthe luminance at a wavelength showing the maximum luminance at eachmeasurement angle as 1. From FIG. 51, it is seen that deviations occurin the spectra depending on the measurement angle.

Then, FIG. 52 shows the measurement results of the organic LED elementhaving the scattering layer. FIG. 53 shows spectral data furthernormalized, taking the luminance at a wavelength showing the maximumluminance at each measurement angle as 1. From FIG. 53, it is seen thatdeviations scarcely occur in the spectra even when the measurement anglechanges. Further, the results of conversion of the above-mentionedspectra to chromaticity coordinates are shown in Table 8 and FIG. 54.

TABLE 8 Measurement No Scattering Layer With Scattering Layer Angle θ xy x y 0° (Front) 0.304 0.595 0.333 0.579 10° 0.305 0.59 0.333 0.579 20°0.302 0.593 0.333 0.579 30° 0.305 0.585 0.333 0.579 40° 0.305 0.5770.331 0.581 50° 0.314 0.566 0.33 0.582 60° 0.316 0.56 0.33 0.582

It is seen that the element having no scattering layer largely changesin color depending on the measurement angle, whereas changes are smallfor the element having the scattering layer. The above has revealed thata further effect of decreasing angle changes in color is obtained, inaddition to the effect of improving the light-extraction efficiencywhich is the original object, by imparting the scattering layer to theelement. The small angle changes in color result in a great advantagethat the seeing angle is not limited, as the light-emitting element.

As known from the above-mentioned evaluation experiments, it has beenproved that the simulations of the invention are correct.

Incidentally, of the scattering layers used herein, cross sections ofones fired at 570° C. and 580° C. were polished, and SEM photographswere taken at a magnification of 10,000×. From the photographs, therelationship between the number of pores and distances from the surfaceof the glass scattering layer to the pores was examined. The laterallength of the SEM photograph was 12.5 μm. Lines were drawn on the SEMphotograph at intervals of 0.25 μm from the surface of the scatteringlayer, and the number of pores found in a frame of 0.25 μm×12.5 μm wascounted. Here, a pore existing over a plurality of frames was counted asexisting in a lower frame. The results thereof are shown in FIG. 55. TheX-axis indicates the distance from the surface of the glass scatteringlayer herein. For example, a point at 0.5 μm shows the number of poresconfirmed in a frame 0.25 μm to 0.5 μm apart measured from the glasssurface of the scattering layer. Further, X=0 shows the number ofconcave portions existing on the surface of the glass scattering layer,as shown in FIG. 7 or FIG. 8. As shown in the graph, it can be confirmedthat the number of pores decreases with an approach to the surface from0.5 μm from the surface, as shown by curve a, in the case of a firingtemperature of 570° C., from 1.25 μm from the surface, as shown by curveb, in the case of a firing temperature of 580° C. Further, in bothcases, no concave portion was confirmed on the surface.

Further, from FIG. 55, it is apparent that the density ρ₃ of thescattering material at a distance x (x≦0.2 μm) from the surface of theabove-mentioned scattering layer including glass and the density ρ₄ ofthe above-mentioned scattering material at a distance x=2 μm satisfyρ₄>ρ₃. Furthermore, FIG. 55 shows the results in the case where thefiring temperature is 570° C. and 580° C. However, even when the firingtemperature was somewhat varied, similar results could be obtained.

Moreover, from FIG. 55, it is also apparent that the density ρ₃ of thescattering material at a distance x (x≦0.2 μm) from the surface of theabove-mentioned scattering layer including glass and the density ρ₅ ofthe above-mentioned scattering material at a distance x=5 μm satisfyρ₅>ρ₃.

Incidentally, the number of pores in the scattering layer fired at 580°C. tends to be more than that of the scattering layer fired at 570° C.However, the cause thereof can not be concluded. As the possibilitythereof, the following two are considered.

(1) In the scattering layer fired at 580° C., pores more expand by ahigher temperature to become easy to count.

(2) The decomposition of organic residues adhered to the glass powdermore proceeds at 580° C. to increase the number of pores.

Then, the presence or absence of the occurrence of precipitated crystalswas examined. When precipitated on the surface of the glass scatteringlayer, the crystals can be easily visually recognized under an opticalmicroscope, because when no crystals are precipitated, the surface ofthe scattering layer is very smooth, and a peculiar point isconspicuous. The difference between the crystals and foreign matter canbe easily judged from the symmetry of the shape and the like. Further,the precipitated crystals in the inside of the glass scattering layercan also be easily distinguished from the pores and foreign matter bythe shape thereof. The results are shown in Table 9. By selecting properfiring conditions such as firing at 570° C., it is possible toprecipitate the crystals only in the inside of the scattering layer andto inhibit the occurrence thereof on the surface.

TABLE 9 Firing Inside of Glass Surface of Glass Temperature ScatteringLayer Scattering Layer 570° C. Observed Not observed 580° C. ObservedNot observed

Incidentally, the pores and the crystals are generated by differentmechanisms, so that it is possible to generate only the pores or onlythe crystals by controlling the glass material, the powder particlesize, the surface state, the firing conditions (atmosphere, pressure) orthe like. For example, crystal precipitation is inhibited by increasinga network former in the glass or increasing an alkali oxide componentfor inhibiting crystal precipitation, and pore generation is inhibitedby firing under reduced pressure.

Example 3 Waviness

Then, Example 3 of the invention will be described.

First, as a sample for measurement, there was prepared one in which ascattering layer was formed on a PD200 substrate, and an Al thin filmhaving a thickness of about 80 nm was further formed thereon by a vapordeposition method. As the scattering layers, six kinds shown in Table 10were used. Glass compositions A, B and C are shown in Table 11 and Table12, respectively.

TABLE 10 Firing Glass Material Temperature Film Thickness 1 A 550° C. 15μm 2 560° C. 15 μm 3 570° C. 15 μm 4 580° C. 15 μm 5 B 550° C. 60 μm 6 C550° C. 30 μm

TABLE 11 A B P₂O₅ 23.1 23.1 B₂O₃ 12 5.5 Li₂O 11.6 11.6 Na₂O 0 4 K₂O 02.5 Bi₂O₃ 16.6 16.6 TiO₂ 8.7 8.7 Nb₂O₅ 17.6 17.6 WO₃ 10.4 10.4 Unit: mol%

TABLE 12 C SiO₂ 5.1 B₂O₃ 24.24 Pb₃O₄ 52.37 BaO 7.81 Al₂O₃ 6.06 TiO₂ 2.71CeO₂ 0.41 Co₃O₄ 0.48 MnO₂ 0.56 CuO 0.26 Unit: mol %

Then, the waviness was measured. As an apparatus, there was used SURFCOM(trade name: 1400D-12) manufactured Tokyo Seimitsu Co., Ltd. Roughnessmeasurement was made at a measuring length of 5.0 mm and a measuringspeed of 0.15 mm/s, taking the short wavelength cutoff value λs as 25.0μm and the long wavelength cutoff value λc as 2.5 mm. The wavinessroughness Ra and the arithmetic average wavelength Rλa are calculatedfrom this measured data in the apparatus based on the JIS 2001 standard(the translated standard of ISO 97). Further, from the data of thewaviness, the surface area was calculated, and the difference from theflat case was compared. Then, the diffuse reflection ratio was measured.In a measuring system, parallel light is allowed to income through oneopening of an integrating sphere, the sample is placed at an openingcorresponding to the opposite corner thereof, and a detecting apparatusof outgoing light is placed at another opening. As the detectingapparatus, there was used a spectro-photometer Lambda 950 manufacturedby Perkin Elmer.

First, spectrometry of total reflection is carried out in a state wherethe other openings are closed, and the reflectivity is calculated usingthat data. The calculation of the reflectivity is performed bymultiplying the spectral data obtained by the spectral distribution of alight source and the color-matching function y(λ). Incidentally, a D65standard light source was used for the light source data, and the dataof 2° field of view was used for the color-matching function.

Then, spectrometry is carried out in a state where the opening of theintegrating sphere, which is placed at a position where light spectrallyreflected outgoes to the sample, is opened, and the reflectivity at thattime is calculated. The reflectivity ion this case shall be called thediffuse reflectivity. Then, the diffuse reflectivity ratio wascalculated by dividing the diffuse reflectivity by the totalreflectivity. The measurement results thereof are as shown in Table 1.

Since there is the scattering material in the glass scattering layer, ametal electrode surface is not visually recognized like a mirrorsurface. However, supposing that scatterability is lowered, it isvisually recognized as a mirror surface, which is possibly unfavorablein terms of the appearance. This time, when the Al film is formed on thescattering layer and observation is made from the Al electrode side, theappearance of the metal electrode can be evaluated without beingaffected by the scattering layer. As shown in Table 13, the diffusereflectivity ratio increases by the waviness, and seeing specularity isrestrained in all cases.

The diffuse reflectivity ratio at the time when the Al film was directlyformed on the glass substrate was measured. As a result, it was 40%, andbecame a large value compared to 38% of material C. However, specularvisibility was apparently restrained to the eye, when the scatteringlayer was formed by material C. However, although the outline of an bodyreflected blurs to be able to restrain specularity in the case ofmaterial C(Ra/λRa=0.0234×10⁻²), the diffuse reflectivity ratioequivalent to or more than the case of material A fired at 580° C.(Ra/λRa=0.556×10⁻²) is more preferred. In that case, the outline of abody reflected is not visually recognized at all.

Example 4 Total Transmittance (Haze Value) of Scattering Layers

The results of measuring the total transmittance of the scatteringlayers will be described below.

Scattering layers having the glass composition shown in Table 1 anddifferent in thickness were prepared on glass substrates. The scatteringlayers have thicknesses of 9 μm, 15 μm and 30 μm, respectively. OrganicLED elements were prepared on these scattering layers, followed byevaluation to evaluate the ratio of the light-extraction efficiency tothe case of having no scattering layer, in the same manner as describedabove. When total transmittance and the haze value were measured usingthe above-mentioned haze meter, a sample is set in the inside of anintegrating sphere 300 as shown in FIG. 56 to prevent loss of the lightpropagating in a lateral direction inside the substrate 101 to performevaluation. The relationship between the film thickness of thescattering layer and the total light transmittance is shown in FIG. 57,and the relationship between the film thickness of the scattering layerand the haze value is shown in FIG. 58.

As shown in the graphs, it is confirmed that the total lighttransmittance decreases and the haze value increases with an increase inthe film thickness of the scattering layer 102. Then, thelight-extraction efficiency ratio (light-extraction ratio) comparing thetotal light transmittance to the case of having no scattering layer isshown in FIG. 59, and the light-extraction efficiency ratio(light-extraction ratio) comparing the haze value to the case of havingno scattering layer is shown in FIG. 60.

The glass material has definite absorption. Accordingly, when the degreeof scattering increases, the light path length passing through in thescattering layer becomes long, resulting in a decrease the extractionefficiency. Conversely, when the scattering is small, the direction oflight can not be changed, so that total reflection can not be inhibited,resulting in a decrease in the extraction efficiency. From these, thereare the total light transmittance and the haze value suitable formaximizing the extraction efficiency.

From the above-mentioned experiment results, the total lighttransmittance is desirably 75% or more. Further, it is desirable thatthis translucent substrate has a haze value of 80 to 87.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be understood by those skilled inthe art that various changes and modifications may be made thereinwithout departing from the spirit and scope of the invention.

The present application is based on Japanese Patent Application No.2007-195797 filed on Jul. 27, 2007, and Japanese Patent Application No.2007-241287 filed on Sep. 18, 2007, the contents of which areincorporated herein by reference.

INDUSTRIAL APPLICABILITY

As has been described above, the electrode-attached translucentsubstrate of the invention has the scattering layer which is excellentin scatterability and high in reliability, so that light-extractionefficiency or incorporation efficiency can be increased to be applicableto light-emitting devices, light-receiving devices and the like.

1. An electrode-attached translucent substrate comprising: a translucentglass substrate; a scattering layer formed over the glass substrate andcomprising a glass which contains: a base material having a firstrefractive index for at least one wavelength of light to be transmitted;and a plurality of scattering materials dispersed in the base materialand having a second refractive index different from that of the basematerial; and a translucent electrode formed over the scattering layerand having a third refractive index equal to or lower than the firstrefractive index, wherein distribution of the scattering materials inthe scattering layer decreases from the inside of the scattering layertoward the translucent electrode.
 2. The translucent substrate accordingto claim 1, satisfying ρ₄>ρ₃, wherein ρ₃ is a density of the scatteringmaterial at a distance x (x≦0.2 μm) from a surface of the scatteringlayer and ρ₄ is a density of the scattering material at a distance xbeing 2 μm.
 3. The translucent substrate according to claim 1, wherein asurface of the scattering layer has waviness constituting a curvedsurface.
 4. The translucent substrate according to claim 3, wherein theratio Ra/Rλa of a waviness roughness Ra of the surface of the scatteringlayer to a wavelength Rλa of the waviness of the surface is from1.0×10⁻³ to 3.0×10⁻².
 5. The translucent substrate according to claim 1,wherein a surface roughness Ra of the surface of the scattering layer is30 nm or less.
 6. The translucent substrate according to claim 1,wherein the content of the scattering material in the scattering layeris at least 1 vol %.
 7. The translucent substrate according to claim 1,wherein the scattering materials are pores.
 8. The translucent substrateaccording to claim 1, wherein the scattering materials are materialparticles having a composition different from that of the base layer. 9.The translucent substrate according to claim 1, wherein the scatteringmaterials are precipitated crystals of a glass constituting the baselayer.
 10. The translucent substrate according to claim 1, wherein thenumber of the scattering materials per 1 mm² of the scattering layer isat least 1×10⁴.
 11. The translucent substrate according to claim 1,wherein the scattering layer has an average thermal expansioncoefficient over the range of 100° C. to 400° C. of 70×10⁻⁷(° C.⁻¹) to95×10⁻⁷(° C.⁻¹), and a glass transition temperature of 450° C. to 550°C.
 12. The translucent substrate according to claim 1, wherein thescattering layer contains 20 to 30 mol % of P₂O₅, 3 to 14 mol % of B₂O₃,10 to 20 mol % of Li₂O, Na₂O and K₂O in terms of total amount thereof,10 to 20 mol % of Bi₂O₃, 3 to 15 mol % of TiO₂, 10 to 20 mol % of Nb₂O₅and 5 to 15 mol % of WO₃.
 13. A process for producing a translucentsubstrate comprising the steps of: preparing a translucent glasssubstrate, forming over the glass substrate a scattering layercomprising: a base material having a first refractive index; and aplurality of scattering materials dispersed in the base material andhaving a second refractive index different from that of the basematerial, and forming a translucent electrode over the scattering layer,wherein the scattering layer forming step includes the steps of:applying a coating material containing a glass powder onto the glasssubstrate, and firing the applied glass powder, and wherein theintralayer distribution of the scattering materials in the scatteringlayer decreases from the inside of the scattering layer toward theoutermost surface thereof.
 14. The process for producing a translucentsubstrate according to claim 13, wherein the firing step includes a stepof firing the glass powder at a temperature which is 60 to 100° C.higher than the glass transition temperature of the applied glassmaterial.
 15. The process for producing a translucent substrateaccording to claim 13, wherein the applying step includes a step ofapplying the glass powder having a particle size D₁₀ of 0.2 μm or moreand D₉₀ of 5 μm or less.
 16. A process for producing an organic LEDelement comprising: the process for producing a translucent substrateaccording to claim 13; a step of forming a layer having a light emittingfunction over the translucent layer as a first electrode; and a step offorming a second electrode over the layer having a light emittingfunction.
 17. The translucent substrate according to claim 1, having awavelength of light to be transmitted being equal to a wavelength ofemitted light of an organic LED element.
 18. An organic LED elementcomprising an organic layer formed over the translucent electrode layerof the translucent substrate according to claim 17 and a reflectiveelectrode formed over the organic layer.
 19. The process for producing atranslucent substrate according to claim 13, wherein the base materialand the scattering materials constituting the scattering layer are abase material having a first refractive index for at least onewavelength of wavelengths of emitted light of an organic LED element anda plurality of scattering materials positioned in the base material andhaving a second refractive index different from that of the basematerial, respectively, and the translucent electrode layer has a thirdrefractive index equal to or lower than the first refractive index atthe wavelength.
 20. A process for producing an organic LED elementcomprising the steps of: forming an organic layer over the translucentelectrode of the translucent substrate according to claim 19, andforming a reflective electrode over the organic layer.